GitLab

To track the state of a BeginMainFrame, SENT and STARTED serve the same
purpose: they indicate that a BeginMainFrame has been issued to the
main-thread, and the main-thread has not responded to that yet. So
remove STARTED state, and use only SENT instead.

Document these states, and also ForcedRedrawOnTimeoutState.

BUG=none

Change-Id: I200337cfe0a8ec7544961b01abf22fbc56eea5d8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1709153
Commit-Queue: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Sunny Sachanandani <sunnyps@chromium.org>
Cr-Commit-Position: refs/heads/master@{#678945}