Composited Animations: Introduce pixel-ref layout tests.

LayoutTests/VirtualTestSuites

 [
   {
     "prefix": "gpu",
     "base": "fast/canvas",
     "args": ["--enable-accelerated-2d-canvas",
              "--disable-display-list-2d-canvas"]
   },
   {
     "prefix": "display_list_2d_canvas",
     "base": "fast/canvas",
@@ skipping 15 matching lines @@
     "args": ["--enable-prefer-compositing-to-lcd-text"]
   },
   {
     "prefix": "prefer_compositing_to_lcd_text",
     "base": "scrollbars",
     "args": ["--enable-prefer-compositing-to-lcd-text"]
   },
   {
     "prefix": "threaded",
     "base": "animations",
-    "args": ["--enable-threaded-compositing"]
+    "args": ["--enable-threaded-compositing",
+             "--disable-composited-antialiasing"]

[dstockwell, 2015/08/06 00:23:19]

Add a comment about why this flag is needed.

[loyso (OOO), 2015/09/14 06:19:07]

1) We already have layer-edge anti-aliasing disabled for android.
2) How can I add comment to a strict JSON file? We don't have a notaion like
"_comment":

   },
   {
     "prefix": "threaded",
     "base": "transitions",
     "args": ["--enable-threaded-compositing"]
   },
   {
     "prefix": "threaded",
     "base": "fast/scroll-behavior",
     "args": ["--enable-threaded-compositing",
@@ skipping 99 matching lines @@
     "base": "fast/workers",
     "args": ["--js-flags=--harmony-sharedarraybuffer",
              "--enable-blink-features=SharedArrayBuffer"]
   },
   {
     "prefix": "trustedeventsdefaultaction",
     "base": "fast/events",
     "args": ["--enable-blink-features=TrustedEventsDefaultAction"]
   }
 ]