CC::Animations should use TimeTicks & TimeDelta to represent time

cc/input/page_scale_animation.cc

Index: cc/input/page_scale_animation.cc
diff --git a/cc/input/page_scale_animation.cc b/cc/input/page_scale_animation.cc
index 7df0244ec0907a1466bc2ab9625c147fe075d754..a216cfd2c60f4568938b58fdd3cd19e2a6cbbb3a 100644
--- a/cc/input/page_scale_animation.cc
+++ b/cc/input/page_scale_animation.cc
@@ -166,33 +166,34 @@ bool PageScaleAnimation::IsAnimationStarted() const {
   return start_time_ >= 0;
 }
 
-void PageScaleAnimation::StartAnimation(double time) {
+void PageScaleAnimation::StartAnimation(base::TimeTicks time) {
   DCHECK_GT(0, start_time_);
-  start_time_ = time;
+  start_time_ = (time - base::TimeTicks()).InSecondsF();
 }
 
-gfx::Vector2dF PageScaleAnimation::ScrollOffsetAtTime(double time) const {
+gfx::Vector2dF PageScaleAnimation::ScrollOffsetAtTime(
+    base::TimeTicks time) const {
   DCHECK_GE(start_time_, 0);
   return ScrollOffsetAt(InterpAtTime(time));
 }
 
-float PageScaleAnimation::PageScaleFactorAtTime(double time) const {
+float PageScaleAnimation::PageScaleFactorAtTime(base::TimeTicks time) const {
   DCHECK_GE(start_time_, 0);
   return PageScaleFactorAt(InterpAtTime(time));
 }
 
-bool PageScaleAnimation::IsAnimationCompleteAtTime(double time) const {
+bool PageScaleAnimation::IsAnimationCompleteAtTime(base::TimeTicks time) const {
   DCHECK_GE(start_time_, 0);
-  return time >= end_time();
+  return (time - base::TimeTicks()).InSecondsF() >= end_time();
 }
 
-float PageScaleAnimation::InterpAtTime(double time) const {
+float PageScaleAnimation::InterpAtTime(base::TimeTicks time) const {
   DCHECK_GE(start_time_, 0);
-  DCHECK_GE(time, start_time_);
+  DCHECK_GE((time - base::TimeTicks()).InSecondsF(), start_time_);
   if (IsAnimationCompleteAtTime(time))
     return 1.f;
-
-  const double normalized_time = (time - start_time_) / duration_;
+  double monotonic_time = (time - base::TimeTicks()).InSecondsF();
+  const double normalized_time = (monotonic_time - start_time_) / duration_;
   return timing_function_->GetValue(normalized_time);
 }