Add ShareGroup to GLES2Implemenation

Add ShareGroup to GLES2Implemenation

The idea is if you don't pass a ShareGroup it will make one.
Otherwise you can do

new_gles2_impl = new GLES2Implemetation(
   ...,
   some_other_gles2_impl_in_same_process->share_group(),
   ...);

TEST=unit test
BUG=120297
TBR=nfullgar@google.com,brettw@chromium.org

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=129555

[greggman, 2012-03-28 21:17:10]

Hey Al, more PREP, PTAL

should I just TBR everyone else?

[apatrick_chromium, 2012-03-28 21:50:57]

LGTM. Though the try bots don't seem to have synced to a revision with
client/ref_counted.

[commit-bot: I haz the power, 2012-03-28 23:26:34]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/gman@chromium.org/9837124/1

[commit-bot: I haz the power, 2012-03-29 01:51:43]

Change committed as 129555