Support Mac frameworks in GN.

This special cases libs ending in ".framework" on Mac and removes the mac-specific hacks in the binary target writer.

BUG=304344
R=scottmg@chromium.org

Review URL: https://codereview.chromium.org/88813005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237622 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237622