Implement OnMemoryStateChange for Various CC Classes

cc/resources/resource_pool.cc

Index: cc/resources/resource_pool.cc
diff --git a/cc/resources/resource_pool.cc b/cc/resources/resource_pool.cc
index 5e6e426871cf63229841e7e75d4b94f731a39033..05591c3b3d7122ae740c2a64f34474b38b7beab9 100644
--- a/cc/resources/resource_pool.cc
+++ b/cc/resources/resource_pool.cc
@@ -469,8 +469,15 @@ void ResourcePool::OnMemoryStateChange(base::MemoryState state) {
       // save memory usage.
       break;
     case base::MemoryState::SUSPENDED:
-      // TODO(tasak): free this component's caches as much as possible before
-      // suspending renderer.
+      // We are only ever SUSPENDED while in the background. While in the
+      // background, ResourcePool already has zero memory limits and should not
+      // be holding any resources that aren't actively in use.
+      DCHECK_EQ(0, unused_resources_.size());

[vmpstr, 2016/09/23 20:59:10]

Are we guaranteed that we receive this signal after we get backgrounded? I'm
curious about order of events here.

[ericrk, 2016/09/23 21:26:15]

My understanding was that we are only suspended while invisible. That said, it
seems fragile to rely on this ordering. Re-structed so that we can handle any
order of calls.

+
+      // The following call will drop additional busy resources. There is no
+      // negative to this other than temporary incorrect accounting, and it
+      // ensures the resource is freed as soon as possible.
+      EvictResourcesNotUsedSince(base::TimeTicks() + base::TimeDelta::Max());
       break;
     case base::MemoryState::UNKNOWN:
       // NOT_REACHED.