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}

• cc/BUILD.gn[diff]
• cc/animation/animation_host.cc[diff]
• cc/animation/animation_host.h[diff]
• cc/cc_tests.gyp[diff]
• cc/layers/layer.cc[diff]
• cc/layers/layer.h[diff]
• cc/layers/layer_impl.cc[diff]
• cc/layers/layer_impl.h[diff]
• cc/layers/layer_utils.cc[diff]
• cc/test/layer_tree_test.cc[diff]
• cc/test/layer_tree_test.h[diff]
• cc/trees/layer_tree_host.cc[diff]
• cc/trees/layer_tree_host.h[diff]
• cc/trees/layer_tree_host_common.cc[diff]
• cc/trees/layer_tree_host_impl.cc[diff]
• cc/trees/layer_tree_host_unittest_animation_timelines.cc[Added - diff]
• cc/trees/layer_tree_impl.cc[diff]
• cc/trees/layer_tree_impl.h[diff]
• cc/trees/property_tree_builder.cc[diff]