Revert of Mac Overlays: Add GPU back-pressure

Revert of Mac Overlays: Add GPU back-pressure (patchset #8 id:140001 of https://codereview.chromium.org/1273563002/ )

Reason for revert:
This broke the WebGL 2.0 prototype on Mac OS -- please see https://code.google.com/p/chromium/issues/detail?id=515696#c16 for details.

Original issue's description:
> Mac Overlays: Add GPU back-pressure
>
> Issue a GL fence after every SwapBuffers. Do not call -[CALayer
> setContents:] with the content being rendered by that SwapBuffers until
> the fence has passed.
>
> Query the previous's frame's GL fence at the beginning of each
> SwapBuffers. Also issue a callback to query the GL fence at the
> mid-point of the VSync period (if there is no subsequent SwapBuffers,
> or if the frame takes more than one VSync to render).
>
> Note that waiting for the GL fence to complete before calling -[CALayer
> setContents] is not required for correctness -- only the expected content
> (everything before the glFlush) will appear in the layer. Rather, the
> reason for waiting for the GL fence is to make the time at which the
> content will appear on-screen more reliable.
>
> Because there may be multiple calls to SwapBuffers in flight, store the
> data necessary to call -[CALayer setContents] in a PendingSwap
> structure. Maintain a queue of these structures.
>
> Because the ImageTransportSurface does not know anything about the
> VSync period, send the CGDirectDisplayID for the attached display to the
> ImageTransportSurface in the AcceleratedSurfaceMsg_BufferPresented IPC
> (which is where the CGL renderer ID is already communicated). Send this
> information instead of the raw VSync parameters so that the updates to
> all windows on a single display may be coalesced into a single callback
> in the future.
>
> Note that this display is the display that is used for vsync by the
> RenderWidgetHostViewMac, so if vsync is disabled, it will be 0.
>
> Separate gfx::ScopedSetGLToRealGLApi into its own header file to
> simplify header orders.
>
> Access the IOSurface of the GLImageIOSurface directly, rather than
> using its ScheduleOverlayPlane method. This simplifies things
> immediately, in that we can reason about the underlying IOSurface's
> lifetime better than weak pointers to images. It will also simplify
> the implementation of partial swap and multiple overlays.
>
> BUG=515696
>
> Committed: https://crrev.com/5c207cac73c835b5f362670d6b46333dfae1f4c4
> Cr-Commit-Position: refs/heads/master@{#342548}

TBR=dcheng@chromium.org,jbauman@chromium.org,tapted@chromium.org,ccameron@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=515696
Committed: https://crrev.com/9f6cac12a46fb8960d4dc25ae5901906697a45f8
Cr-Commit-Position: refs/heads/master@{#342566}

[Ken Russell (switch to Gerrit), 2015-08-09 18:54:20]

Created Revert of Mac Overlays: Add GPU back-pressure

[commit-bot: I haz the power, 2015-08-09 18:54:28]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1280033004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1280033004/1

[commit-bot: I haz the power, 2015-08-09 18:54:51]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-09 18:55:36]

Patchset 1 (id:??) landed as
https://crrev.com/9f6cac12a46fb8960d4dc25ae5901906697a45f8
Cr-Commit-Position: refs/heads/master@{#342566}