Support MSAA in the picture debugger

Add radio buttons for setting the GL sample count to 0 ("off"), 4 or
16.

Change the default mode of the GL widget to MSAA4. Previous behavior
corresponded to "off".

BUG=1459
R=robertphillips@google.com

Author: kkinnunen@nvidia.com

Review URL: https://chromiumcodereview.appspot.com/21752002

git-svn-id: http://skia.googlecode.com/svn/trunk@10509 2bbb7eff-a529-9590-31e7-b0007b416f81
8 files changed