Revert 287747 "Make SingleThreadProxy a SchedulerClient"

Revert 287747 "Make SingleThreadProxy a SchedulerClient"
This is a speculative revert to see if issues on Mac bots get resolved.

BrowserTest.WindowOpenClose is e.g. failing on this assert:
ASSERTION FAILED: !active || m_layerTreeView

> Make SingleThreadProxy a SchedulerClient
>
> This makes ui::Compositor no longer in charge of
> scheduling commits and draws, deferring it to cc::Scheduler.
>
> Other compositors that use SingleThreadProxy are left calling composite
> synchronously and now pass a flag to indicate that this is their
> intention.  This patch doesn't remove synchronous composite, but now
> makes it mutually exclusive with scheduling.
>
> BUG=329552, 287250
>
> Review URL: https://codereview.chromium.org/134623005

TBR=enne@chromium.org

Review URL: https://codereview.chromium.org/441343002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@287766 0039d316-1c4b-4281-b951-d872f2087c98