This CL:
- Makes app windows and browser windows use different assets for the header and window controls
- Removes the separator for the window controls
- Changes FrameCaptionButton so that the buttons use separate assets for the button background and the button icon.

BUG=297187
TEST=Visual by kuscher@
R=jamescook@chromium.org

Review URL: https://codereview.chromium.org/178193004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253576 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253576