Remove pdf files on Mac and use 2x pngs in the omnibox.

Side effect: The default favicon is now an empty page instead
of a globe.

BUG=134372,111101
TEST=icons in omnibox are hidpi and generally match the look
on non-mac platforms.
TBR=avi

Review URL: https://chromiumcodereview.appspot.com/10660021

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@144334 0039d316-1c4b-4281-b951-d872f2087c98