am a6aca3e0: Merge change 25435 into eclair

Merge commit 'a6aca3e094719b181c9858aa57d6c2160c5cb16a' into eclair-plus-aosp

* commit 'a6aca3e094719b181c9858aa57d6c2160c5cb16a':
  disable backbuffer preservation when possible, which may improve performance a bit