Implemented ScopedFakeTime, faking rtc::TimeNanos.

webrtc/base/timeutils.h

Index: webrtc/base/timeutils.h
diff --git a/webrtc/base/timeutils.h b/webrtc/base/timeutils.h
index 222d5c26e4774efc568736bd2f9fcfa417978ed1..5d2c938a5b4b7830dfd0f1171a6514c5c61c0f6c 100644
--- a/webrtc/base/timeutils.h
+++ b/webrtc/base/timeutils.h
@@ -18,6 +18,19 @@
 
 namespace rtc {
 
+namespace test {
+
+class FakeTimeInterface {
+ public:
+  virtual uint64_t TimeNanos() = 0;
+  virtual ~FakeTimeInterface() {}
+};
+
+// Allows overriding the system clocks in tests, see faketime.h.
+void SetFakeTime(FakeTimeInterface* f);
+
+}  // namespace test
+
 static const int64_t kNumMillisecsPerSec = INT64_C(1000);
 static const int64_t kNumMicrosecsPerSec = INT64_C(1000000);
 static const int64_t kNumNanosecsPerSec = INT64_C(1000000000);