In most cases, this does not matter, especially if assigning to the
source variable again:
x = Abs(x)

But there are cases where it matters, e.g. when being used as argument
to a template function:
DCHECK_EQ(x, Abs(x));
which would currently *not* fail for x==kMinInt.

R=tebbi@chromium.org

Change-Id: Ia5abfe164db602b80a34548e0bf9b22033b77c6e
Reviewed-on: https://chromium-review.googlesource.com/568028Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46586}