Added log messages for some important call setup events:

 - First audio RTP packet sent / received
 - First RTP packet of the first video frame sent / received
 - Last RTP packet of the first video frame sent / received
These timestamps should make it easier to measure how fast the call
becomes established from the user's perspective.

Review URL: https://codereview.webrtc.org/1765443002

Cr-Commit-Position: refs/heads/master@{#12287}
diff --git a/webrtc/base/BUILD.gn b/webrtc/base/BUILD.gn
index bc6cb38..4c344fd 100644
--- a/webrtc/base/BUILD.gn
+++ b/webrtc/base/BUILD.gn
@@ -133,6 +133,7 @@
     "md5digest.cc",
     "md5digest.h",
     "mod_ops.h",
+    "onetimeevent.h",
     "optional.h",
     "platform_file.cc",
     "platform_file.h",
diff --git a/webrtc/base/base.gyp b/webrtc/base/base.gyp
index a5f0f7b..52f2ffe 100644
--- a/webrtc/base/base.gyp
+++ b/webrtc/base/base.gyp
@@ -105,6 +105,7 @@
         'md5digest.cc',
         'md5digest.h',
         'mod_ops.h',
+        'onetimeevent.h',
         'optional.h',
         'platform_file.cc',
         'platform_file.h',
diff --git a/webrtc/base/base_tests.gyp b/webrtc/base/base_tests.gyp
index caef35c..ec38933 100644
--- a/webrtc/base/base_tests.gyp
+++ b/webrtc/base/base_tests.gyp
@@ -79,6 +79,7 @@
           'multipart_unittest.cc',
           'nat_unittest.cc',
           'network_unittest.cc',
+          'onetimeevent_unittest.cc',
           'optional_unittest.cc',
           'optionsfile_unittest.cc',
           'pathutils_unittest.cc',
diff --git a/webrtc/base/onetimeevent.h b/webrtc/base/onetimeevent.h
new file mode 100644
index 0000000..9708b4b
--- /dev/null
+++ b/webrtc/base/onetimeevent.h
@@ -0,0 +1,62 @@
+/*
+ *  Copyright (c) 2016 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_ONETIMEEVENT_H_
+#define WEBRTC_BASE_ONETIMEEVENT_H_
+
+#include "webrtc/base/scoped_ptr.h"
+#include "webrtc/base/criticalsection.h"
+#include "webrtc/typedefs.h"
+
+namespace webrtc {
+// Provides a simple way to perform an operation (such as logging) one
+// time in a certain scope.
+// Example:
+//   OneTimeEvent firstFrame;
+//   ...
+//   if (firstFrame()) {
+//     LOG(LS_INFO) << "This is the first frame".
+//   }
+class OneTimeEvent {
+ public:
+  OneTimeEvent() {}
+  bool operator()() {
+    rtc::CritScope cs(&critsect_);
+    if (happened_) {
+      return false;
+    }
+    happened_ = true;
+    return true;
+  }
+
+ private:
+  bool happened_ = false;
+  rtc::CriticalSection critsect_;
+};
+
+// A non-thread-safe, ligher-weight version of the OneTimeEvent class.
+class ThreadUnsafeOneTimeEvent {
+ public:
+  ThreadUnsafeOneTimeEvent() {}
+  bool operator()() {
+    if (happened_) {
+      return false;
+    }
+    happened_ = true;
+    return true;
+  }
+
+ private:
+  bool happened_ = false;
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_BASE_ONETIMEEVENT_H_
diff --git a/webrtc/base/onetimeevent_unittest.cc b/webrtc/base/onetimeevent_unittest.cc
new file mode 100644
index 0000000..4ebc139
--- /dev/null
+++ b/webrtc/base/onetimeevent_unittest.cc
@@ -0,0 +1,33 @@
+/*
+ *  Copyright 2016 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/gunit.h"
+#include "webrtc/base/onetimeevent.h"
+
+namespace webrtc {
+
+TEST(OneTimeEventTest, ThreadSafe) {
+  OneTimeEvent ot;
+
+  // The one time event is expected to evaluate to true only the first time.
+  EXPECT_TRUE(ot());
+  EXPECT_FALSE(ot());
+  EXPECT_FALSE(ot());
+}
+
+TEST(OneTimeEventTest, ThreadUnsafe) {
+  ThreadUnsafeOneTimeEvent ot;
+
+  EXPECT_TRUE(ot());
+  EXPECT_FALSE(ot());
+  EXPECT_FALSE(ot());
+}
+
+}  // namespace webrtc