commit 7f4335afc67aec5a50d7eb1285f12c04ec41f8cb
author glebl <glebl@chromium.org> Wed Jul 06 23:13:53 2016
committer Commit bot <commit-bot@chromium.org> Wed Jul 06 23:16:12 2016
tree fd6467dfb80f471e089c0c952ff15b0e52fb3825
parent 2eaf5026683bacf68be54dbacd4dab91dee4f4a2

This change adds "alpha" option to PaintWorklet.

Usage example:
registerPaint('foo', class {
  static get alpha() { return true; }

  paint() { }
});

If true (default) the backdrop of the rendering context is transparent, if false the backdrop is opaque.

css-houdini-drafts github issue: https://github.com/w3c/css-houdini-drafts/issues/220

BUG=578252

TEST=third_party/WebKit/LayoutTests/csspaint/background-image-alpha.html

Review-Url: https://codereview.chromium.org/2077413005
Cr-Commit-Position: refs/heads/master@{#403967}