Some of the warnings that are disabled on windows are not actually trigger any failures and can be simply enabled without changing any source code.

It is our intent to keep the warning level in blink close to the to the default chromium warning level, so we should re-enable these warnings for windows.

BUG=312287

Review URL: https://codereview.chromium.org/63073002

git-svn-id: svn://svn.chromium.org/blink/trunk@161685 bbb929c8-8fbe-4397-9dbb-9b2b20218538