Implement frames() timing function

cc/animation/timing_function.cc

Index: cc/animation/timing_function.cc
diff --git a/cc/animation/timing_function.cc b/cc/animation/timing_function.cc
index d0d55ad54fa75f6357fc3318229048a7d49e54f0..0271c57bb44ca99e41266ce0bbb6576487d852ae 100644
--- a/cc/animation/timing_function.cc
+++ b/cc/animation/timing_function.cc
@@ -131,4 +131,41 @@ float StepsTimingFunction::GetStepsStartOffset() const {
   }
 }
 
+std::unique_ptr<FramesTimingFunction> FramesTimingFunction::Create(int frames) {
+  return base::WrapUnique(new FramesTimingFunction(frames));
+}
+
+FramesTimingFunction::FramesTimingFunction(int frames) : frames_(frames) {}
+
+FramesTimingFunction::~FramesTimingFunction() {}
+
+TimingFunction::Type FramesTimingFunction::GetType() const {
+  return Type::FRAMES;
+}
+
+float FramesTimingFunction::GetValue(double t) const {
+  return static_cast<float>(GetPreciseValue(t));
+}
+
+std::unique_ptr<TimingFunction> FramesTimingFunction::Clone() const {
+  return base::WrapUnique(new FramesTimingFunction(*this));
+}
+
+void FramesTimingFunction::Range(float* min, float* max) const {
+  *min = 0.0f;
+  *max = 1.0f;
+}
+
+float FramesTimingFunction::Velocity(double x) const {
+  return 0.0f;
+}
+
+double FramesTimingFunction::GetPreciseValue(double t) const {
+  const double frames = static_cast<double>(frames_);
+  double output_progress = std::floor(frames * t) / (frames - 1);
+  if (t <= 1 && output_progress > 1)
+    output_progress = 1;
+  return output_progress;
+}
+
 }  // namespace cc