Make CSSStyleImageValue a member of CanvasImageSource.

This will make it possible to call BaseRenderingContext2D.drawImage with CSSOM Style Image object as an argument.

BUG=567358
TEST=third_party/WebKit/LayoutTests/csspaint/paint2d-image.html

Review-Url: https://codereview.chromium.org/2351363002
Cr-Commit-Position: refs/heads/master@{#422010}
15 files changed