Switch to double for time calculations using playback rate.

media/base/time_source.h

Index: media/base/time_source.h
diff --git a/media/base/time_source.h b/media/base/time_source.h
index 71fe858e8c97eda36d605b73f6cbf5f1e39815ca..d025de2a6ccb53cdebee6b1f71dd78eab6b11c50 100644
--- a/media/base/time_source.h
+++ b/media/base/time_source.h
@@ -27,7 +27,7 @@ class MEDIA_EXPORT TimeSource {
   // Updates the current playback rate. It is expected that values from
   // CurrentMediaTime() will eventually reflect the new playback rate (e.g., the
   // media time will advance at half speed if the rate was set to 0.5f).
-  virtual void SetPlaybackRate(float playback_rate) = 0;
+  virtual void SetPlaybackRate(double playback_rate) = 0;
 
   // Sets the media time to start ticking from. Only valid to call while the
   // time source is not ticking.