Increase MSVC warning level to 4. There are some exceptions, a subset of the exceptions used by Chromium. They didn't seem to be useful warnings. In code which we don't change much, like the preprocessor, I just suppressed the warnings in the specific files rather than changing the code. There should be no functional changes in this patch. Review URL: https://codereview.appspot.com/5570066 git-svn-id: https://angleproject.googlecode.com/svn/trunk@964 736b8ea6-26fd-11df-bfd4-992fa37f6226