views: Cleanup PaintRestoredClientEdge() function.

- Pass clang-format to make the code more readable, better indentation.
- Better docs.
- Reorganize the code to make more sense of the code flow.
- Use GetImageSkiaNamed() instead of calling ToImageSkia() everywhere.
- append _center prefix to some variables.

BUG=None
TEST=content_shell still works
R=jamescook@chromium.org

Review URL: https://codereview.chromium.org/97633002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238293 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238293