Revert of Added GetCpuTime to base/ to get total CPU time consumed by process for perf tests. (patchset #24 id:440001 of https://codereview.webrtc.org/2695743003/ )

Reason for revert:
The GetThreadCpuTimeTest.SingleThread and .TwoThreads tests are unfortunately flaky on Mac (maybe other platforms).  See for example:

https://build.chromium.org/p/client.webrtc/builders/Mac%20Asan/builds/11271/steps/rtc_unittests%20on%20Mac-10.11/logs/stdio

https://build.chromium.org/p/client.webrtc/builders/Mac64%20Debug/builds/10395/steps/rtc_unittests%20on%20Mac-10.11/logs/stdio

https://build.chromium.org/p/client.webrtc/builders/Mac%20Asan/builds/11271/steps/rtc_unittests%20on%20Mac-10.11/logs/stdio

Since it's late, I'll have to revert the CL to get the tree and trybots green (instead of only disabling the failing tests).

Original issue's description:
> Added GetCpuTime to base/ to get total CPU time consumed by process for perf tests.
>
> BUG=webrtc:7095
>
> Review-Url: https://codereview.webrtc.org/2695743003
> Cr-Commit-Position: refs/heads/master@{#16665}
> Committed: https://chromium.googlesource.com/external/webrtc/+/3ff474b72ba1b34027e8391b1014c2838af445d4

TBR=sprang@webrtc.org,mflodman@webrtc.org,deadbeef@webrtc.org,nisse@webrtc.org,kjellander@webrtc.org,ilnik@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=webrtc:7095

Review-Url: https://codereview.webrtc.org/2698333004
Cr-Commit-Position: refs/heads/master@{#16679}
diff --git a/webrtc/base/BUILD.gn b/webrtc/base/BUILD.gn
index 558ce58..4e03dc7 100644
--- a/webrtc/base/BUILD.gn
+++ b/webrtc/base/BUILD.gn
@@ -682,8 +682,6 @@
     sources = [
       # Also use this as a convenient dumping ground for misc files that are
       # included by multiple targets below.
-      "cpu_time.cc",
-      "cpu_time.h",
       "fakeclock.cc",
       "fakeclock.h",
       "fakenetwork.h",
@@ -765,7 +763,6 @@
       "bytebuffer_unittest.cc",
       "byteorder_unittest.cc",
       "copyonwritebuffer_unittest.cc",
-      "cpu_time_unittest.cc",
       "criticalsection_unittest.cc",
       "event_tracer_unittest.cc",
       "event_unittest.cc",
diff --git a/webrtc/base/cpu_time.cc b/webrtc/base/cpu_time.cc
deleted file mode 100644
index 5fce366..0000000
--- a/webrtc/base/cpu_time.cc
+++ /dev/null
@@ -1,114 +0,0 @@
-/*
- *  Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
- *
- *  Use of this source code is governed by a BSD-style license
- *  that can be found in the LICENSE file in the root of the source
- *  tree. An additional intellectual property rights grant can be found
- *  in the file PATENTS.  All contributing project authors may
- *  be found in the AUTHORS file in the root of the source tree.
- */
-
-#include "webrtc/base/cpu_time.h"
-#include "webrtc/base/logging.h"
-#include "webrtc/base/timeutils.h"
-
-#if defined(WEBRTC_LINUX)
-#include <time.h>
-#elif defined(WEBRTC_MAC)
-#include <sys/resource.h>
-#include <sys/types.h>
-#include <sys/times.h>
-#include <mach/thread_info.h>
-#include <mach/thread_act.h>
-#include <mach/mach_init.h>
-#include <unistd.h>
-#elif defined(WEBRTC_WIN)
-#include <windows.h>
-#endif
-
-#if defined(WEBRTC_WIN)
-namespace {
-// FILETIME resolution is 100 nanosecs.
-const int64_t kNanosecsPerFiletime = 100;
-}  // namespace
-#endif
-
-namespace rtc {
-
-int64_t GetProcessCpuTimeNanos() {
-#if defined(WEBRTC_LINUX)
-  struct timespec ts;
-  if (clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &ts) == 0) {
-    return ts.tv_sec * kNumNanosecsPerSec + ts.tv_nsec;
-  } else {
-    LOG_ERR(LS_ERROR) << "clock_gettime() failed.";
-  }
-#elif defined(WEBRTC_MAC)
-  struct rusage rusage;
-  if (getrusage(RUSAGE_SELF, &rusage) == 0) {
-    return rusage.ru_utime.tv_sec * kNumNanosecsPerSec +
-           rusage.ru_utime.tv_usec * kNumNanosecsPerMicrosec;
-  } else {
-    LOG_ERR(LS_ERROR) << "getrusage() failed.";
-  }
-#elif defined(WEBRTC_WIN)
-  FILETIME createTime;
-  FILETIME exitTime;
-  FILETIME kernelTime;
-  FILETIME userTime;
-  if (GetProcessTimes(GetCurrentProcess(), &createTime, &exitTime, &kernelTime,
-                      &userTime) != 0) {
-    return ((static_cast<uint64_t>(userTime.dwHighDateTime) << 32) +
-            userTime.dwLowDateTime) *
-           kNanosecsPerFiletime;
-  } else {
-    LOG_ERR(LS_ERROR) << "GetProcessTimes() failed.";
-  }
-#else
-  // Not implemented yet.
-  static_assert(
-      false, "GetProcessCpuTimeNanos() platform support not yet implemented.");
-#endif
-  return -1;
-}
-
-int64_t GetThreadCpuTimeNanos() {
-#if defined(WEBRTC_LINUX)
-  struct timespec ts;
-  if (clock_gettime(CLOCK_THREAD_CPUTIME_ID, &ts) == 0) {
-    return ts.tv_sec * kNumNanosecsPerSec + ts.tv_nsec;
-  } else {
-    LOG_ERR(LS_ERROR) << "clock_gettime() failed.";
-  }
-#elif defined(WEBRTC_MAC)
-  thread_basic_info_data_t info;
-  mach_msg_type_number_t count = THREAD_BASIC_INFO_COUNT;
-  if (thread_info(mach_thread_self(), THREAD_BASIC_INFO, (thread_info_t)&info,
-                  &count) == KERN_SUCCESS) {
-    return info.user_time.seconds * kNumNanosecsPerSec +
-           info.user_time.microseconds * kNumNanosecsPerMicrosec;
-  } else {
-    LOG_ERR(LS_ERROR) << "thread_info() failed.";
-  }
-#elif defined(WEBRTC_WIN)
-  FILETIME createTime;
-  FILETIME exitTime;
-  FILETIME kernelTime;
-  FILETIME userTime;
-  if (GetThreadTimes(GetCurrentThread(), &createTime, &exitTime, &kernelTime,
-                     &userTime) != 0) {
-    return ((static_cast<uint64_t>(userTime.dwHighDateTime) << 32) +
-            userTime.dwLowDateTime) *
-           kNanosecsPerFiletime;
-  } else {
-    LOG_ERR(LS_ERROR) << "GetThreadTimes() failed.";
-  }
-#else
-  // Not implemented yet.
-  static_assert(
-      false, "GetProcessCpuTimeNanos() platform support not yet implemented.");
-#endif
-  return -1;
-}
-
-}  // namespace rtc
diff --git a/webrtc/base/cpu_time.h b/webrtc/base/cpu_time.h
deleted file mode 100644
index 87e9418..0000000
--- a/webrtc/base/cpu_time.h
+++ /dev/null
@@ -1,28 +0,0 @@
-/*
- *  Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
- *
- *  Use of this source code is governed by a BSD-style license
- *  that can be found in the LICENSE file in the root of the source
- *  tree. An additional intellectual property rights grant can be found
- *  in the file PATENTS.  All contributing project authors may
- *  be found in the AUTHORS file in the root of the source tree.
- */
-
-#ifndef WEBRTC_BASE_CPU_TIME_H_
-#define WEBRTC_BASE_CPU_TIME_H_
-
-#include <stdint.h>
-
-namespace rtc {
-
-// Returns total CPU time of a current process in nanoseconds.
-// Time base is unknown, therefore use only to calculate deltas.
-int64_t GetProcessCpuTimeNanos();
-
-// Returns total CPU time of a current thread in nanoseconds.
-// Time base is unknown, therefore use only to calculate deltas.
-int64_t GetThreadCpuTimeNanos();
-
-}  // namespace rtc
-
-#endif  // WEBRTC_BASE_CPU_TIME_H_
diff --git a/webrtc/base/cpu_time_unittest.cc b/webrtc/base/cpu_time_unittest.cc
deleted file mode 100644
index cb025ea..0000000
--- a/webrtc/base/cpu_time_unittest.cc
+++ /dev/null
@@ -1,108 +0,0 @@
-/*
- *  Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
- *
- *  Use of this source code is governed by a BSD-style license
- *  that can be found in the LICENSE file in the root of the source
- *  tree. An additional intellectual property rights grant can be found
- *  in the file PATENTS.  All contributing project authors may
- *  be found in the AUTHORS file in the root of the source tree.
- */
-
-#include <memory>
-#include <algorithm>
-#include "webrtc/base/cpu_time.h"
-#include "webrtc/base/platform_thread.h"
-#include "webrtc/base/timeutils.h"
-#include "webrtc/test/gtest.h"
-#include "webrtc/system_wrappers/include/cpu_info.h"
-
-namespace {
-const int kAllowedErrorMillisecs = 30;
-const int kProcessingTimeMillisecs = 300;
-
-// Consumes approximately kProcessingTimeMillisecs of CPU time.
-bool WorkingFunction(void* counter_pointer) {
-  int64_t* counter = reinterpret_cast<int64_t*>(counter_pointer);
-  *counter = 0;
-  int64_t stop_time = rtc::SystemTimeNanos() +
-                      kProcessingTimeMillisecs * rtc::kNumNanosecsPerMillisec;
-  while (rtc::SystemTimeNanos() < stop_time) {
-    (*counter)++;
-  }
-  return false;
-}
-}  // namespace
-
-namespace rtc {
-
-TEST(GetProcessCpuTimeTest, SingleThread) {
-  int64_t start_time_nanos = GetProcessCpuTimeNanos();
-  int64_t counter;
-  WorkingFunction(reinterpret_cast<void*>(&counter));
-  EXPECT_GT(counter, 0);
-  int64_t duration_nanos = GetProcessCpuTimeNanos() - start_time_nanos;
-  //  Should be about kProcessingTimeMillisecs.
-  EXPECT_NEAR(duration_nanos,
-              kProcessingTimeMillisecs * kNumNanosecsPerMillisec,
-              kAllowedErrorMillisecs * kNumNanosecsPerMillisec);
-}
-
-TEST(GetProcessCpuTimeTest, TwoThreads) {
-  int64_t start_time_nanos = GetProcessCpuTimeNanos();
-  int64_t counter1;
-  int64_t counter2;
-  PlatformThread thread1(WorkingFunction, reinterpret_cast<void*>(&counter1),
-                         "Thread1");
-  PlatformThread thread2(WorkingFunction, reinterpret_cast<void*>(&counter2),
-                         "Thread2");
-  thread1.Start();
-  thread2.Start();
-  thread1.Stop();
-  thread2.Stop();
-
-  EXPECT_GE(counter1, 0);
-  EXPECT_GE(counter2, 0);
-  int64_t duration_nanos = GetProcessCpuTimeNanos() - start_time_nanos;
-  const uint32_t kWorkingThreads = 2;
-  uint32_t used_cores =
-      std::min(webrtc::CpuInfo::DetectNumberOfCores(), kWorkingThreads);
-  // Two working threads for kProcessingTimeMillisecs consume double CPU time
-  // if there are at least 2 cores.
-  EXPECT_NEAR(duration_nanos,
-              used_cores * kProcessingTimeMillisecs * kNumNanosecsPerMillisec,
-              used_cores * kAllowedErrorMillisecs * kNumNanosecsPerMillisec);
-}
-
-TEST(GetThreadCpuTimeTest, SingleThread) {
-  int64_t start_times_nanos = GetThreadCpuTimeNanos();
-  int64_t counter;
-  WorkingFunction(reinterpret_cast<void*>(&counter));
-  EXPECT_GT(counter, 0);
-  int64_t duration_nanos = GetThreadCpuTimeNanos() - start_times_nanos;
-  EXPECT_NEAR(duration_nanos,
-              kProcessingTimeMillisecs * kNumNanosecsPerMillisec,
-              kAllowedErrorMillisecs * kNumNanosecsPerMillisec);
-}
-
-TEST(GetThreadCpuTimeTest, TwoThreads) {
-  int64_t start_time_nanos = GetThreadCpuTimeNanos();
-  int64_t counter1;
-  int64_t counter2;
-  PlatformThread thread1(WorkingFunction, reinterpret_cast<void*>(&counter1),
-                         "Thread1");
-  PlatformThread thread2(WorkingFunction, reinterpret_cast<void*>(&counter2),
-                         "Thread2");
-  thread1.Start();
-  thread2.Start();
-  thread1.Stop();
-  thread2.Stop();
-
-  EXPECT_GE(counter1, 0);
-  EXPECT_GE(counter2, 0);
-  int64_t duration_nanos = GetThreadCpuTimeNanos() - start_time_nanos;
-  // This thread didn't do any work.
-  EXPECT_NEAR(duration_nanos, 0,
-              kAllowedErrorMillisecs * kNumNanosecsPerMillisec);
-}
-
-}  // namespace rtc