Add versions of stroke, fill, and clip to CanvasRenderingContext2D that take a Path parameter.

The spec reference is:
http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#dom-context-2d-fill

This partially addresses bug 330506. The rest of these functions need to be added to completely close that bug, which I plan to do in a following CL:
 - drawSystemFocusRing(path, element);
 - drawCustomFocusRing(path, element);
 - isPointInPath(path, x, y);
 - isPointInStroke(path, x, y);
 - scrollPathIntoView(path);

BUG=330506

Review URL: https://codereview.chromium.org/137353004

git-svn-id: svn://svn.chromium.org/blink/trunk@167705 bbb929c8-8fbe-4397-9dbb-9b2b20218538