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

cc/scheduler/delay_based_time_source.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/scheduler/delay_based_time_source.h"
 
 #include <algorithm>
 #include <cmath>
 
 #include "base/bind.h"
@@ skipping 15 matching lines @@
 // immediate interval change.  kPhaseChangeThreshold is the fraction of the
 // interval that will trigger an immediate phase change.  If the changes are
 // within the thresholds, the change will take place on the next tick.  If
 // either change is outside the thresholds, the next tick will be canceled and
 // reissued immediately.
 static const double kIntervalChangeThreshold = 0.25;
 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) {
   return make_scoped_refptr(new DelayBasedTimeSource(interval, task_runner));
 }
 
 DelayBasedTimeSource::DelayBasedTimeSource(
     base::TimeDelta interval, base::SingleThreadTaskRunner* task_runner)
     : client_(NULL),
       last_tick_time_(base::TimeTicks() - interval),
@@ skipping 199 matching lines @@
   task_runner_->PostDelayedTask(FROM_HERE,
                                 base::Bind(&DelayBasedTimeSource::OnTimerFired,
                                            weak_factory_.GetWeakPtr()),
                                 delay);
 
   next_parameters_.tick_target = new_tick_target;
   current_parameters_ = next_parameters_;
 }
 
 }  // namespace cc