[PDF] Add debug assert to detect failure of GDI cache hack.

If we start hitting this check, then it's likely that something has regressed in WebKit.

Original CL from arthurhsu@chromium.org: http://codereview.appspot.com/5322063/

Review URL: http://codereview.appspot.com/5320062

git-svn-id: http://skia.googlecode.com/svn/trunk@2581 2bbb7eff-a529-9590-31e7-b0007b416f81
1 file changed