Flip BLAST flag.

This flag will enable the BLASTBufferQueue adapter for use by ViewRootImpl.
BLASTSync and the BLASTBufferQueue in SurfaceView are still behind seperate flags.

Bug: 168506246
Test: Days of manual testing on multiple devices (stressed: app switching, rotation, SurfaceView, PIP, Split-screen). Multiple presubmits. 5 passing runs of flicker. Systrace inspection. App startup perf tests. Inspection of jankstats from experiment based flip in R dogfood.
Change-Id: I2b6e37884d938d327479977becbbce8e38e521f0