Make Keyframe use TimeTicks/TimeDelta to represent time instead of double.

cc/base/time_util.h

 // Copyright 2014 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.
 
 #ifndef CC_BASE_TIME_UTIL_H_
 #define CC_BASE_TIME_UTIL_H_
 
 namespace base {
 class TimeDelta;
 }
 
 namespace cc {
 
 class CC_EXPORT TimeUtil {
  public:
   static base::TimeDelta Scale(base::TimeDelta time_delta, double value) {
     return base::TimeDelta::FromInternalValue(static_cast<int64>(
         static_cast<double>(time_delta.ToInternalValue()) * value));
   }
 
+  static double Divide(base::TimeDelta dividend, base::TimeDelta divisor) {
+    return static_cast<double>(dividend.ToInternalValue()) /
+           static_cast<double>(divisor.ToInternalValue());
+  }
+
   static base::TimeDelta Mod(base::TimeDelta dividend,
                              base::TimeDelta divisor) {
     return base::TimeDelta::FromInternalValue(dividend.ToInternalValue() %
                                               divisor.ToInternalValue());
   }
 };
 
 }  // namespace cc
 
 #endif  // CC_BASE_TIME_UTIL_H_