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Add DCHECK() to verify that every impl-frame started is also terminated
as expected: either a frame is submitted, or no-damage is explicitly
reported.

Also, add 'R' to the debug-log for a reset, and always report 'e' for
end, even for an invalid sequence-number.

BUG=1035382

Change-Id: I1aeab1453fa0c1b80a02b2f1795ab898be71a060
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1976912Reviewed-by: Xida Chen <xidachen@chromium.org>
Commit-Queue: Xida Chen <xidachen@chromium.org>
Auto-Submit: Sadrul Chowdhury <sadrul@chromium.org>
Cr-Commit-Position: refs/heads/master@{#726688}