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If the main-thread is blocked until a vsync's deadline, then the
reporter is cloned, submitted, and marked as having 'partial update'.
However, it is possible for the main-thread to respond, after the
deadline, with 'no updates' (or 'no damage'). In such cases, the frame
that was submitted did not really have a 'partial update' So reset the
flag that was set, so that the metrics are reported correctly.

To do this:
 . When a reporter is cloned, track the link between the original
   reporter and the cloned reporter.
 . When the original reporter is no longer blocked, check if the frame
   ended with 'no updates'. If it did, then unset the 'partial update'
   flag from the cloned reporter.
 . The cloned reporter can be displayed before the original reporter has
   a response from the main-thread. In such cases, keep the cloned
   reporter alive until the original reporter receives the main-thread
   response, so that the 'partial update' flag can be unset if
   necessary.

BUG=1115376

Change-Id: Ib2e8b0bc1fc924e7442625c4cb82dfa5a88ced95
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2385929
Commit-Queue: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Behdad Bakhshinategh <behdadb@chromium.org>
Reviewed-by: Xida Chen <xidachen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804528}