Remove hang watching of deprecated BrowserThreads.

This is a partial reland of https://chromium-review.googlesource.com/c/chromium/src/+/705775

That CL caused issue 768886 (spike in hang reports). I suspect this
was caused by a change in enum IDs rather than this change to the
hang watching code and this CL will help narrow down the cause.

R=asvitkine@chromium.org

NOPRESUBMIT=TRUE (shuffling of code using deprecated BrowserThread IDs)

Bug: 689520,768886
Change-Id: Id7bf1c7b5f5d34c4b1e7b1e71e9b015725695997
Reviewed-on: https://chromium-review.googlesource.com/743846
Commit-Queue: Gabriel Charette <gab@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512509}
2 files changed