Fixes:
 * conformance/canvas/canvas-test.html
 * conformance/canvas/draw-static-webgl-to-multiple-canvas-test.html
 * conformance/canvas/to-data-url-test.html
 * conformance/context/context-attribute-preserve-drawing-buffer.html
 * conformance/context/premultiplyalpha-test.html
 * conformance/extensions/oes-texture-float-with-canvas.html
 * conformance/extensions/oes-texture-half-float-with-canvas.html
 * conformance/textures/misc/gl-pixelstorei.html
 * conformance/textures/misc/tex-image-canvas-corruption.html

Change-Id: Iab37a211c498ed0eece4c1748cf8b4ab6c0f53e0
Reviewed-on: https://chromium-review.googlesource.com/274444Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>