Stop turning off the overlap map with --enable-bleeding-edge-rendering-fast-paths

We are doing this because we do not intend to launch turning off the overlap map just yet. The primary reason is that at present, turning off the overlap map causes too much of an increase in rasterization cost on top pages.

BUG=351471

Review URL: https://codereview.chromium.org/196023004

git-svn-id: svn://svn.chromium.org/blink/trunk@169041 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Throw DOM exception if OfflineAudioContext cannot be created.

Test added to catch this case.
BUG=351277

Review URL: https://codereview.chromium.org/194813006

git-svn-id: svn://svn.chromium.org/blink/trunk@169043 bbb929c8-8fbe-4397-9dbb-9b2b20218538