Revert of Disable kEnableGpuMemoryBufferCompositorResources on Mac

Revert of Disable kEnableGpuMemoryBufferCompositorResources on Mac (patchset #1 id:1 of https://codereview.chromium.org/1435133003/ )

Reason for revert:
This is no longer needed now that 48 has branched and https://codereview.chromium.org/1463853002/ is landed.

Original issue's description:
> Disable kEnableGpuMemoryBufferCompositorResources on Mac
>
> This caused an uptick in crashes due to GpuMemoryBuffers failing to
> allocate.
>
> BUG=554541
> TBR=reveman
>
> Committed: https://crrev.com/c5b6a85810bd669a3916587ac4d70ac566351258
> Cr-Commit-Position: refs/heads/master@{#359396}

TBR=
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=554541
Committed: https://crrev.com/c871e30d3ab91600b4081b3b90f5aa209ef64409
Cr-Commit-Position: refs/heads/master@{#361248}

[ccameron, 2015-11-24 03:38:39]

Created Revert of Disable kEnableGpuMemoryBufferCompositorResources on Mac

[commit-bot: I haz the power, 2015-11-24 03:39:05]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1470213002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1470213002/1

[commit-bot: I haz the power, 2015-11-24 03:42:17]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-11-24 03:43:45]

Patchset 1 (id:??) landed as
https://crrev.com/c871e30d3ab91600b4081b3b90f5aa209ef64409
Cr-Commit-Position: refs/heads/master@{#361248}