Do not give GPU memory to backgrounded compositors.

cc/output/context_provider.h

Index: cc/output/context_provider.h
diff --git a/cc/output/context_provider.h b/cc/output/context_provider.h
index 6db326d7f9a570210120bc74385a2daf51fabda2..0a794d77d6882648cb776fab0b4304843bbdd4d3 100644
--- a/cc/output/context_provider.h
+++ b/cc/output/context_provider.h
@@ -78,9 +78,8 @@ class ContextProvider : public base::RefCountedThreadSafe<ContextProvider> {
 
   // Sets a callback to be called when the memory policy changes. This should be
   // called from the same thread that the context is bound to.
-  typedef base::Callback<void(
-    const cc::ManagedMemoryPolicy& policy,
-    bool discard_backbuffer_when_not_visible)> MemoryPolicyChangedCallback;
+  typedef base::Callback<void(const cc::ManagedMemoryPolicy& policy)>
+      MemoryPolicyChangedCallback;
   virtual void SetMemoryPolicyChangedCallback(
       const MemoryPolicyChangedCallback& memory_policy_changed_callback) = 0;