A notification will be sent to chromium-dev if this sticks.

Some blink baselines shift due to different rounding behaviour. In the
majority of cases, this means the Windows and Mac/Linux baselines now
become identical.

This also switches win_clang bots to use MSVC as compiler, to make sure
things stay compilable with MSVC.

Known problems:
* Build times without goma are slower (but you can do goma builds with
  debug info now, which are faster).
* Incremental linking of webcore.dll doesn't work (see crbug.com/717207
  and crbug.com/560475)

BUG=82385,709690

Change-Id: I67421a5aee2259cf98b93d34d69a3314dbd98304
Reviewed-on: https://chromium-review.googlesource.com/588077


Commit-Queue: Hans Wennborg <hans@chromium.org>
Reviewed-by: Brett Wilson <brettw@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#490494}