Fix onTrimMemory for HardwareRenderer

 Also fixes detachFunctor possibly drawing after return

 Bug: 15189843
 Bug: 15990672

Change-Id: I64c48cb674c461a8eeaba407b697e09f72c98ce3
diff --git a/libs/hwui/TreeInfo.h b/libs/hwui/TreeInfo.h
index 083100e..9746ac53 100644
--- a/libs/hwui/TreeInfo.h
+++ b/libs/hwui/TreeInfo.h
@@ -65,7 +65,8 @@
         // but don't evaluate animators and such as if it isn't detached as a
         // MODE_FULL will follow shortly.
         MODE_MAYBE_DETACHING,
-        // TODO: TRIM_MEMORY?
+        // Destroy all hardware resources, including DisplayListData, in the tree.
+        MODE_DESTROY_RESOURCES,
     };
 
     explicit TreeInfo(TraversalMode mode, RenderState& renderState)