RTCStatsCollector: timestamps updated.

Using a timestamp based on a timer that is monotonically increasing for
the cache, so that cache's freshness can be checked regardless of if
system clock is modified.

Using a system clock for the stats' timestamp, which needs to be
relative to UNIX epoch (Jan 1, 1970, UTC).

This CL removes the dependency on faketiming.h.

BUG=chromium:627816
NOTRY=True

Review-Url: https://codereview.webrtc.org/2299643002
Cr-Commit-Position: refs/heads/master@{#13997}
diff --git a/webrtc/stats/rtcstats_unittest.cc b/webrtc/stats/rtcstats_unittest.cc
index 44e75c4..1d4e016 100644
--- a/webrtc/stats/rtcstats_unittest.cc
+++ b/webrtc/stats/rtcstats_unittest.cc
@@ -17,8 +17,8 @@
 
 class RTCTestStats : public RTCStats {
  public:
-  RTCTestStats(const std::string& id, double timestamp)
-      : RTCStats(id, timestamp),
+  RTCTestStats(const std::string& id, int64_t timestamp_us)
+      : RTCStats(id, timestamp_us),
         m_int32("mInt32"),
         m_uint32("mUint32"),
         m_int64("mInt64"),
@@ -72,8 +72,8 @@
 
 class RTCChildStats : public RTCStats {
  public:
-  RTCChildStats(const std::string& id, double timestamp)
-      : RTCStats(id, timestamp),
+  RTCChildStats(const std::string& id, int64_t timestamp_us)
+      : RTCStats(id, timestamp_us),
         child_int("childInt") {}
 
   WEBRTC_RTCSTATS_IMPL(RTCStats, RTCChildStats,
@@ -86,8 +86,8 @@
 
 class RTCGrandChildStats : public RTCChildStats {
  public:
-  RTCGrandChildStats(const std::string& id, double timestamp)
-      : RTCChildStats(id, timestamp),
+  RTCGrandChildStats(const std::string& id, int64_t timestamp_us)
+      : RTCChildStats(id, timestamp_us),
         grandchild_int("grandchildInt") {}
 
   WEBRTC_RTCSTATS_IMPL(RTCChildStats, RTCGrandChildStats,
@@ -99,9 +99,9 @@
 const char RTCGrandChildStats::kType[] = "grandchild-stats";
 
 TEST(RTCStatsTest, RTCStatsAndMembers) {
-  RTCTestStats stats("testId", 42.0);
+  RTCTestStats stats("testId", 42);
   EXPECT_EQ(stats.id(), "testId");
-  EXPECT_EQ(stats.timestamp(), 42.0);
+  EXPECT_EQ(stats.timestamp_us(), static_cast<int64_t>(42));
   std::vector<const RTCStatsMemberInterface*> members = stats.Members();
   EXPECT_EQ(members.size(), static_cast<size_t>(14));
   for (const RTCStatsMemberInterface* member : members) {