Bug 983650 - Temporarily mark b2g webgl reftests tests as random. a=test-only

These tests fail on the current test machines but pass on the new ones. Mark them as random for now until we finish the transition to the new machines.
Bug 980537 - Only store FakeBackstagePass instances in mThisObjects. r=khuey, a=1.2.x+
Bug 990794 - Crash on ovrfl in SharedBuffer::Create(). r=roc, a=1.2.x+
Bug 990794 - Crash on ovrfl in AllocateAudioBlock. r=roc, a=1.2.x+