Canvas 2D: Remove CompositeOperator and WebBlendMode parameters in drawImageInternal().

fillInternal() and strokeInternal() don't have those parameters.
CompositeOperator and WebBlendMode parameters exists due to
drawImageFromRect(), which is non-standard API and will maybe deprecated.
Give up the optimization for only drawImageFromRect(), because it's confused
why drawImageInternal() doesn't set current global composite before calling
drawVideo().

In addition, include some clean-up.
1. remove redundant "blink::".
2. merge fullCanvasCompositedFill() with fullCanvasCompositedStroke().

Review URL: https://codereview.chromium.org/645693004

git-svn-id: svn://svn.chromium.org/blink/trunk@183704 bbb929c8-8fbe-4397-9dbb-9b2b20218538