cc: Use HighResNow as timebase if it is fast and reliable

cc/scheduler/delay_based_time_source.cc

Index: cc/scheduler/delay_based_time_source.cc
diff --git a/cc/scheduler/delay_based_time_source.cc b/cc/scheduler/delay_based_time_source.cc
index d150c717a12561a5a401aeb52b8e0baf7e95fcd3..00515b72f7678938b45a6f43a454787192d3eef2 100644
--- a/cc/scheduler/delay_based_time_source.cc
+++ b/cc/scheduler/delay_based_time_source.cc
@@ -33,6 +33,27 @@ static const double kPhaseChangeThreshold = 0.25;
 
 }  // namespace
 
+// The following methods correspond to the DelayBasedTimeSource that uses
+// the base::TimeTicks::HighResNow as the timebase.
+scoped_refptr<DelayBasedTimeSourceHighRes> DelayBasedTimeSourceHighRes::Create(
+    base::TimeDelta interval,
+    base::SingleThreadTaskRunner* task_runner) {
+  return make_scoped_refptr(
+      new DelayBasedTimeSourceHighRes(interval, task_runner));
+}
+
+DelayBasedTimeSourceHighRes::DelayBasedTimeSourceHighRes(
+    base::TimeDelta interval, base::SingleThreadTaskRunner* task_runner)
+    : DelayBasedTimeSource(interval, task_runner) {}
+
+DelayBasedTimeSourceHighRes::~DelayBasedTimeSourceHighRes() {}
+
+base::TimeTicks DelayBasedTimeSourceHighRes::Now() const {
+  return base::TimeTicks::HighResNow();
+}
+
+// The following methods correspond to the DelayBasedTimeSource that uses
+// the base::TimeTicks::Now as the timebase.
 scoped_refptr<DelayBasedTimeSource> DelayBasedTimeSource::Create(
     base::TimeDelta interval,
     base::SingleThreadTaskRunner* task_runner) {