CC Animations: Redirect all compositor animation requests to AnimationHost.

1) Use AnimationHost's AnimationRegistrar instance if new system enabled.
2) Use AnimationPlayer's LayerAnimationController instance if new system enabled.

Previous episode: https://codereview.chromium.org/947033002/
Next episode:
https://codereview.chromium.org/1009233002/

In general: The compositor should not need to worry about servicing animations.
A step towards AnimationHost/AnimationPlayer/AnimationTimeline decoupling.

BUG=394777
R=ajuma@chromium.org
R=vollick@chromium.org
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1010663002

Cr-Commit-Position: refs/heads/master@{#337309}

diff --git a/cc/BUILD.gn b/cc/BUILD.gn
index 2d640ea..719fcf9 100644
--- a/cc/BUILD.gn
+++ b/cc/BUILD.gn

@@ -805,6 +805,7 @@
     "trees/layer_tree_host_pixeltest_tiles.cc",
     "trees/layer_tree_host_unittest.cc",
     "trees/layer_tree_host_unittest_animation.cc",
+    "trees/layer_tree_host_unittest_animation_timelines.cc",
     "trees/layer_tree_host_unittest_context.cc",
     "trees/layer_tree_host_unittest_copyrequest.cc",
     "trees/layer_tree_host_unittest_damage.cc",