Merge changes Ia9b2ced0,I7cccfffc into gb-ub-photos-bryce

* changes:
  Class to simplify use of GalleryBitmapPool for decoding Bitmaps.
  Allow prefetch for cache, reducing priority for prefetched images.
tree: cf64c13a1b6e2271d4298975a94ac3cffc0fb0dd
  1. gallerycommon/
  2. jni_mosaic/
  3. src/
  4. src_pd/
  5. tests/
  6. tests_camera/