Use global references for Bitmap AndroidPixelRefs

bug:9621717

Because we're no longer holding onto Bitmaps Java side during
DisplayList lifetime, use global refs to keep the backing byte arrays
around.

Adds back bitmap buffer passing + native ref management removed by
3b748a44

Adds back globalRef-ing removed by
f890fab5

Change-Id: Ia59ba42f05bea6165aec2b800619221a8083d580