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* Adds a flag for disabling -checkdiscard failures
* Contains fix for assertions being removed when code coverage
  is enabled.
* Contains fix needed for vertical class merging

Bug: 1040534
Change-Id: I6e5eb6242a6126fd4293920bff5267149fabbe1b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2489729
Commit-Queue: Sam Maier <smaier@chromium.org>
Auto-Submit: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Sam Maier <smaier@chromium.org>
Cr-Commit-Position: refs/heads/master@{#821326}