Fix the 1px transparent corners in the Windows app window title bar.

This CL fixes the drawing of the shell window frame view to not draw a 1px gap
into the corners of the title bar.

BUG=317922

Review URL: https://codereview.chromium.org/117863002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241788 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 241788