Animations: Port ProgrammaticScrollAnimator to use compositor timelines

LayoutTests/VirtualTestSuites

Index: LayoutTests/VirtualTestSuites
diff --git a/LayoutTests/VirtualTestSuites b/LayoutTests/VirtualTestSuites
index f827b30319172483ab547d2c6421e2b2c05b12a0..3584492a1b0e26215ca09b24060a53e96651d3f3 100644
--- a/LayoutTests/VirtualTestSuites
+++ b/LayoutTests/VirtualTestSuites
@@ -47,6 +47,13 @@
              "--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"]