Support Canvas2D resetTransform method.

Canvas v5 supports resetTransform.
http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#dom-context-2d-currenttransform

BUG=277110

TEST=fast/canvas/canvas-resetTransform.html

Review URL: https://chromiumcodereview.appspot.com/23531011

git-svn-id: svn://svn.chromium.org/blink/trunk@157521 bbb929c8-8fbe-4397-9dbb-9b2b20218538