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This fixes the compilation problems on ios and corrects
a couple typos. Compare patch sets 1 and 4 to see the differences between
the original commit and the relands.

Original change's description:
> Basic implementation and tests for HangWatcher.
>
> This class is a successor to ThreadWatcher which aims to be more
> versatile and provide a larger coverage for hang watching.
>
> Bug: 1034046
> Change-Id: I365fe8824eb34c37c75e6ddf6874ff26ecd494c6
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2008189
> Commit-Queue: Oliver Li <olivierli@chromium.org>
> Reviewed-by: François Doray <fdoray@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#736080}

Change-Id: I4785c8c489678fd537a0105d65419673fe383aa4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2026316
Auto-Submit: Oliver Li <olivierli@chromium.org>
Reviewed-by: François Doray <fdoray@chromium.org>
Commit-Queue: Oliver Li <olivierli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#736521}