Don't enforce maximum dialog size for browser modal dialogs.

These dialogs are not contained by the browser window, so allow them to have whatever size they want to have.

BUG=288493

Review URL: https://codereview.chromium.org/24265007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227820 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227820