GitLab

Make cc::SoftwareImageDecodeController, cc::GpuImageDecodeController, cc::ResourcePool, and cc::StagingBufferPool MemoryCoordinatorClient.

- implement OnMemoryStateChange for background renderer's purge +
  suspend. So the method reduces memory only when state == SUSPENDED.
- intent-to-implement-and-ship of background renderer's purge + suspend is
  https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/DK189tnM8l4
- one of the documents attached in the above intent is
  https://docs.google.com/document/d/1EgLimgxWK5DGhptnNVbEGSvVn6Q609ZJaBkLjEPRJvI/edit?usp=sharing

BUG=635419
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_precise_blink_rel

Review-Url: https://codereview.chromium.org/2286583002
Cr-Commit-Position: refs/heads/master@{#418834}