Define step timing function for the cc animation framework.

cc/animation/timing_function.h

Index: cc/animation/timing_function.h
diff --git a/cc/animation/timing_function.h b/cc/animation/timing_function.h
index 69d1cc9fb5c43203cb0f79949adb3415fc216a2a..5ee9e9534a4f39b88d01f3fcc74bcf2132792585 100644
--- a/cc/animation/timing_function.h
+++ b/cc/animation/timing_function.h
@@ -81,6 +81,30 @@ class CC_EXPORT EaseInOutTimingFunction {
   DISALLOW_IMPLICIT_CONSTRUCTORS(EaseInOutTimingFunction);
 };
 
+class CC_EXPORT StepsTimingFunction : public TimingFunction {
+ public:
+  enum StepAtPosition { Start, Middle, End };

[ajuma, 2014/12/17 16:32:56]

This doesn't seem to be used anywhere. Were you planning on using it instead of
steps_start_offset? (It seems nicer to use the enum if these are the only
offsets we need to support.) 

If the enum is going to be used, let's make this an enum class since these are
now allowed (see
https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/Q5WmkAImanc).

[loyso (OOO), 2014/12/18 01:53:05]

I forgot to erase this enum. I had the initial implementation (not presented
here) using enums. See my comment below.

+
+  static scoped_ptr<StepsTimingFunction> Create(int steps,
+                                                float steps_start_offset);
+  ~StepsTimingFunction() override;
+
+  float GetValue(double t) const override;
+  scoped_ptr<TimingFunction> Clone() const override;
+
+  void Range(float* min, float* max) const override;
+  float Velocity(double time) const override;
+
+ protected:
+  StepsTimingFunction(int steps, float steps_start_offset);
+
+ private:
+  int steps_;
+  float steps_start_offset_;
+
+  DISALLOW_ASSIGN(StepsTimingFunction);
+};
+
 }  // namespace cc
 
 #endif  // CC_ANIMATION_TIMING_FUNCTION_H_