Don't check the framebuffer status every time we flush when we're on Chromium;

Don't check the framebuffer status every time we flush when we're on Chromium;
this reduces the number of unnecessary command buffer flushes by about 50%
for page loads when doing Ganesh rendering, since we do a flush on clear.

BUG=

Committed: http://code.google.com/p/skia/source/detail?r=12421

[humper, 2013-11-27 17:22:58]

ptal

[bsalomon, 2013-11-27 17:48:01]

lgtm

[commit-bot: I haz the power, 2013-11-27 18:01:41]

CQ is trying da patch. Follow status at
https://skia-tree-status.appspot.com/cq/humper@google.com/92103002/1

[commit-bot: I haz the power, 2013-11-27 18:13:20]

Change committed as 12421