Currently, when we draws GPU decoded Video on accelerated 2D Canvas, chromium
reads back pixel from GPU and then uploads the pixel to GPU to make a SkBitmap.
It's so inefficient for both speed and battery. On the other hand, only Android
copies GPU-GPU in this case, but Android doesn't have cache mechanism which
SkCanvasVideoRenderer provides.

This CL makes all platforms copy gpu-gpu with cache mechanism. Cache mechanism
is useful when 2d canvas draws a video frame many times.
e.g. http://craftymind.com/factory/html5video/CanvasVideo.html

In addition, fix white video background on Android when not loaded. Other platforms
draw black background thanks to SkCanvasVideoRenderer::Paint().

In detail of the changes;
1. Implement gpu-gpu copy in SkCanvasVideoRenderer::Paint() like previous
WebMediaPlayerAndroid::paint().
2. Move duplicated GPU code on WebMediaPlayerImpl and WebMediaPlayerAndroid to
SkCanvasVideoRenderer.

Perf data on i5 IvyBridge
blink_perf.all:Canvas_draw-video-to-hw-accelerated-canvas-2d
15.8x speed up: 116.27 runs/s -> 1847.23 runs/s
NOTE: measure after disabling cache in SkCanvasVideoRenderer

BUG=401058, 263667

Review URL: https://codereview.chromium.org/445013002

Cr-Commit-Position: refs/heads/master@{#310577}