Implemented ScopedFakeTime, faking rtc::TimeNanos.

webrtc/base/timeutils_unittest.cc

Index: webrtc/base/timeutils_unittest.cc
diff --git a/webrtc/base/timeutils_unittest.cc b/webrtc/base/timeutils_unittest.cc
index 0971c037fa551a8c6bca1fe9403a839b6748460f..754a8df9547121568d27b893ec3908283502552b 100644
--- a/webrtc/base/timeutils_unittest.cc
+++ b/webrtc/base/timeutils_unittest.cc
@@ -13,6 +13,7 @@
 #include "webrtc/base/helpers.h"
 #include "webrtc/base/thread.h"
 #include "webrtc/base/timeutils.h"
+#include "webrtc/base/faketime.h"
 
 namespace rtc {
 
@@ -205,4 +206,27 @@ TEST_F(TmToSeconds, TestTmToSeconds) {
   TestTmToSeconds(100000);
 }
 
+TEST(FakeTime, TestScoping) {
+  static const uint64_t kMaxDuration = rtc::kNumNanosecsPerSec;
+  uint64_t before = rtc::TimeNanos();
+  {
+    test::ScopedFakeTime fake_time(10000);
+    EXPECT_EQ(rtc::TimeNanos(), 10000u);
+    fake_time.AdvanceTime(15);
+    EXPECT_EQ(rtc::TimeNanos(), 10015u);
+  }
+  {
+    test::ScopedFakeTime fake_time;
+    uint64_t t = rtc::TimeNanos();
+    EXPECT_LE(before, t);
+    EXPECT_LE(t, before + kMaxDuration);
+    fake_time.AdvanceTime(17);
+    EXPECT_EQ(rtc::TimeNanos(), t + 17);
+  }
+
+  uint64_t after = rtc::TimeNanos();
+  EXPECT_LE(before, after);
+  EXPECT_LE(after - before, kMaxDuration);
+}
+
 }  // namespace rtc