cc: Adding DidFinishImplFrame to LTHI.
This change moves the responsibility of clearing state inside the LTHI after an
impl frame is finished from the thread proxies to the LTHI class. This makes
WillBeginImplFrame and DidFinishImplFrame a logical pair.
This CL also;
* Adds a test that checks the number of WillBeginImplFrame
calls matches the DidFinishImplFrame calls.
* Cleans up classes in cc/test/layer_tree_test.h around WillBeginImplFrame.
* Removes the UpdateCurrentBeginFrameArgs / ResetCurrentBeginFrameArgs methods.
* Fixes a bug where STP was calling ResetCurrentBeginFrameArgs twice every frame.
BUG=346230,481810
R=brianderson,enne
Review URL: https://codereview.chromium.org/
1111743002
Cr-Commit-Position: refs/heads/master@{#328689}