Animations: Port ProgrammaticScrollAnimator to use compositor timelines

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 29 matching lines @@
     "base": "transitions",
     "args": ["--enable-threaded-compositing"]
   },
   {
     "prefix": "threaded",
     "base": "fast/scroll-behavior",
     "args": ["--enable-threaded-compositing",
              "--enable-prefer-compositing-to-lcd-text"]
   },
   {
+    "prefix": "threaded",
+    "base": "fast/scroll-behavior",

[ajuma, 2015/07/22 13:38:29]

How does having two virtual test suites with the same prefix+base work (since we
already have virtual/threaded/fast/scroll-behavior, defined above)? That is,
will virtual/threaded/fast/scroll-behavior run with the args above, or the ones
below, or somehow run twice? In any case, please change the prefix to something
like "threaded_animation_timelines" to avoid confusion.

[loyso (OOO), 2015/07/23 01:18:04]

Done.

+    "args": ["--enable-threaded-compositing",
+             "--enable-compositor-animation-timelines",
+             "--enable-prefer-compositing-to-lcd-text"]
+  },
+  {
     "prefix": "stable",
     "base": "webexposed",
     "args": ["--stable-release-mode"]
   },
   {
     "prefix": "stable",
     "base": "http/tests/serviceworker/webexposed",
     "args": ["--stable-release-mode"]
   },
   {
@@ skipping 82 matching lines @@
     "base": "media/mediasession",
     "args": ["--enable-blink-features=MediaSession"]
   },
   {
     "prefix": "sharedarraybuffer",
     "base": "fast/workers",
     "args": ["--js-flags=--harmony-sharedarraybuffer",
              "--enable-blink-features=SharedArrayBuffer"]
   }
 ]