Introduce separate client and init path for single-threaded cc

Introduce separate client and init path for single-threaded cc

The chromium compositor can be used in either a single-threaded fashion
or multi-threaded. The requirements, APIs and responsibilities of the embedder
are different for these two modes. Some users of cc only use one path
or the other. This adds a separate client interface and initialization
path for code that only uses the single threaded path.

Having a dedicated client for the single threaded path will make it
possible to get rid of the WebGraphicsContext3DSwapBuffersClient which
will then make it easier to break cc's dependency on WGC3D.

R=piman
BUG=181120
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=233483

[jamesr, 2013-11-06 23:49:36]

piman@ - review plz :)

enne/danakj/etc - this changes the LayerTreeHost initialization to be more
explicit about threaded vs not. hopefully we'll be able to migrate more callers
over to only use one init path as time goes on

sievers - i'm removing some nascent g_impl_thread code from the android browser
compositor setup here. it's runtime dead since there's no way to set the thread,
but there isn't much of it so feel free to add it back if/when someone is
interested in bringing up that path on android.

[piman, 2013-11-07 00:15:11]

LGTM, this is cool.

[piman, 2013-11-07 00:16:37]

On 2013/11/07 00:15:11, piman wrote:
> LGTM, this is cool.

(BTW you missed a digit in the BUG= line)

[commit-bot: I haz the power, 2013-11-07 00:32:39]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/jamesr@chromium.org/61823008/1

[enne (OOO), 2013-11-07 00:39:00]

lgtm2, this is really nice cleanup.

[commit-bot: I haz the power, 2013-11-07 05:01:34]

Change committed as 233483