Change --enable-app-shims to --disable-app-shims

Since app shims are now enabled in stable, invert the function of this
switch.

BUG=168080

Review URL: https://codereview.chromium.org/105923005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242711 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 242711