Revert of content: Enable native GpuMemoryBuffers by default on MacOSX.

Revert of content: Enable native GpuMemoryBuffers by default on MacOSX. (patchset #6 id:100001 of https://codereview.chromium.org/1165823003/)

Reason for revert:
This change caused many mac layouttests to fail, see:
https://storage.googleapis.com/chromium-layout-test-archives/WebKit_Mac10_10/107/layout-test-results/results.html
http://test-results.appspot.com/dashboards/flakiness_dashboard.html#tests=fast%2Foverflow%2Fborder-radius-clipping.html

Reverting locally fixed this issue.

Original issue's description:
> content: Enable native GpuMemoryBuffers by default on MacOSX.
>
> This eliminates the need for texture uploads to initialize
> tile textures on MacOSX.
>
> BUG=486922
>
> Committed: https://crrev.com/ab11fd094eb5eb8913a87b9f12497cab0725c73a
> Cr-Commit-Position: refs/heads/master@{#336502}

TBR=avi@chromium.org,ccameron@chromium.org,piman@chromium.org,reveman@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=486922
Committed: https://crrev.com/1f9990d034b73856aaea66f8fc93ac4af9bd1943
Cr-Commit-Position: refs/heads/master@{#336506}

[pdr., 2015-06-28 03:12:04]

Created Revert of content: Enable native GpuMemoryBuffers by default on MacOSX.

[pdr., 2015-06-28 03:12:48]

The CQ bit was checked by pdr@chromium.org

[commit-bot: I haz the power, 2015-06-28 03:12:51]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1219603002/1

[commit-bot: I haz the power, 2015-06-28 03:13:15]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-28 03:14:10]

Patchset 1 (id:??) landed as
https://crrev.com/1f9990d034b73856aaea66f8fc93ac4af9bd1943
Cr-Commit-Position: refs/heads/master@{#336506}