Please apply appropriate OSs label. Thank you.

M63 is branching soon, we will be taking only critical merges. It would be great to have a fix ASAP.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/232c1b8b462051105fbc870db7218e90bb4956ab

commit 232c1b8b462051105fbc870db7218e90bb4956ab
Author: Becca Hughes <beccahughes@chromium.org>
Date: Thu Oct 12 20:01:54 2017

Media Engagement: Fix when history is cleared before a playback

If the history is cleared between a navigation and a playback it
can cause scores over 100. This refactors the contents observer
to commit data in a single transaction when the user navigates
to another origin, playback is recorded or the observer is
destroyed. Some of the histogram tests also needed to be updated
since they don't take into account uncommitted data.

BUG= 773290 
NOTRY=true  # win7_chromium_rel_ng issue tracked in 774136

Change-Id: I55014932e8457d94a1071d0f593dad8b695cd7a7
Reviewed-on: https://chromium-review.googlesource.com/709814
Commit-Queue: Becca Hughes <beccahughes@chromium.org>
Reviewed-by: Nathan Parker <nparker@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Cr-Commit-Position: refs/heads/master@{#508411}
[modify] https://crrev.com/232c1b8b462051105fbc870db7218e90bb4956ab/chrome/browser/media/media_engagement_browsertest.cc
[modify] https://crrev.com/232c1b8b462051105fbc870db7218e90bb4956ab/chrome/browser/media/media_engagement_contents_observer.cc
[modify] https://crrev.com/232c1b8b462051105fbc870db7218e90bb4956ab/chrome/browser/media/media_engagement_contents_observer.h
[modify] https://crrev.com/232c1b8b462051105fbc870db7218e90bb4956ab/chrome/browser/media/media_engagement_contents_observer_unittest.cc
[modify] https://crrev.com/232c1b8b462051105fbc870db7218e90bb4956ab/chrome/browser/safe_browsing/safe_browsing_navigation_observer.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9755707f1d676bfb1a395ef7a4cc17ac165affd0

commit 9755707f1d676bfb1a395ef7a4cc17ac165affd0
Author: Becca Hughes <beccahughes@chromium.org>
Date: Thu Oct 12 20:15:44 2017

Media Engagement: Wipe all data

Wipe all MEI data once crrev.com/c/709814 has landed.

BUG= 773290 
NOTRY=true  # win7_chromium_rel_ng issue tracked in 774136

Change-Id: I6bb50d5f246a2833086e23cf9f7840c2efb511c4
Reviewed-on: https://chromium-review.googlesource.com/716226
Commit-Queue: Becca Hughes <beccahughes@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Cr-Commit-Position: refs/heads/master@{#508432}
[modify] https://crrev.com/9755707f1d676bfb1a395ef7a4cc17ac165affd0/chrome/browser/media/media_engagement_service.cc

beccahughes@ do we need any additional checkin's to M63, if not can we please mark the bug as fixed.

[Auto-generated comment by a script] We noticed that this issue is targeted for M-63; it appears the fix may have landed after branch point, meaning a merge might be required. Please confirm if a merge is required here - if so add Merge-Request-63 label, otherwise remove Merge-TBD label. Thanks.

If no merge is needed to M63, please remove Merge-TBD label.