Prepare for -Wall for third-party code, -Wextra for chromium_code
This lands patch set 16 of https://codereview.chromium.org/1551753002/
(reviewed there), except for the changes to build/common.gypi and
build/config/compiler/BUILD.gn. The changes to these two files are likely
to break some bot I don't know about, and I don't want to keep reverting
and relanding all these files. So this lands the parts that are hopefully
harmless separately.
BUG=573250
TBR=thestig
Review URL: https://codereview.chromium.org/1557733002
Cr-Commit-Position: refs/heads/master@{#367252}
32 files changed
