Revert "mac: Run A/B experiment on SharedMemory mechanism for resource buffers."

This reverts commit e0e2fd398f3d07c8eebbe662d71a0f9286862476.
I believe this CL introduced these layout test failures: http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Mac%20Oilpan/builds/25790

BUG=None
TBR=erikchen

Review URL: https://codereview.chromium.org/1407933008

Cr-Commit-Position: refs/heads/master@{#356557}
5 files changed