Revert of Mac Overlays: Make ImageTransportSurfaceOverlayMac observe GPU switches...

Revert of Mac Overlays: Make ImageTransportSurfaceOverlayMac observe GPU switches (patchset #1 id:1 of https://codereview.chromium.org/1291703002/ )

Reason for revert:
Broke compile. http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Mac10.9%20%28retina%29/builds/4403

Original issue's description:
> Mac Overlays: Make ImageTransportSurfaceOverlayMac observe GPU switches
>
> When the GPU switches, create a new OpenGL context, to see which GL
> renderer it uses. Whenever a context is made current to the surface,
> ensure that the context is using the appropriate renderer.
>
> Ideally, the GpuSwitchingManager should be able to tell the observers
> which GL renderer to use, but that is not currently wired up.
>
> BUG=519097
>
> Committed: https://crrev.com/0009e1ea4154c5a20fffa3cf47b0b29c23a6f7e2
> Cr-Commit-Position: refs/heads/master@{#343277}

TBR=tapted@chromium.org,ccameron@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=519097

Review URL: https://codereview.chromium.org/1294733002

Cr-Commit-Position: refs/heads/master@{#343315}