Implement new overlay style for options pages.

I've attached screenshots in the bug. The changes covered in this CL are:
- background radial gradient.
- dialog panel animation when clicking on modally blocked area.
- text color
- title font size.
- x close button visuals and placement.
- size and placement of action buttons.
- dialog internal padding.
- border radius
- drop shadow

BUG=116312
TEST=Test the new dialogs on the options page.

Review URL: https://chromiumcodereview.appspot.com/9625006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@126414 0039d316-1c4b-4281-b951-d872f2087c98