Fixed issue where HardwareBufferRenderer was not preserving contents

Updated RenderProxy creation to pass false for the opaque flag
in order to avoid an unnecessary canvas->clear invocation within
SkiaPipeline::draw

Fixes: 275398000
Test: Added test to HardwareBufferRendererTests
Change-Id: I5f884240439bf3e57500ed1404f31fbe2ea122fa
2 files changed