Disabled pinch zooming in non-browser Aura windows.

Pinch zoom should not affect native-looking UI. This patch disabled zoom
in all cases except for the browser view.

BUG=232098

Review URL: https://codereview.chromium.org/134683004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247843 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247843