Implement frames() timing function

cc/animation/timing_function.cc

 // Copyright 2012 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/animation/timing_function.h"
 
 #include <memory>
 
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
@@ skipping 109 matching lines @@
     case StepPosition::MIDDLE:
       return 0.5;
     case StepPosition::END:
       return 0;
     default:
       NOTREACHED();
       return 1;
   }
 }
 
+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_);
+  return MathUtil::ClampToRange(std::floor(frames * t) / (frames - 1), 0.0,
+                                1.0);
+}
+
 }  // namespace cc