Allow layers to signal that additional sequences are needed before surface destruction

cc/surfaces/surface.h

Index: cc/surfaces/surface.h
diff --git a/cc/surfaces/surface.h b/cc/surfaces/surface.h
index ffa50420c083b8ed2e984b8b74e9236b4cdae0d7..18195748df332833067aeb81df3a629cfff52ee9 100644
--- a/cc/surfaces/surface.h
+++ b/cc/surfaces/surface.h
@@ -17,6 +17,7 @@
 #include "cc/output/copy_output_request.h"
 #include "cc/quads/render_pass_id.h"
 #include "cc/surfaces/surface_id.h"
+#include "cc/surfaces/surface_sequence.h"
 #include "cc/surfaces/surfaces_export.h"
 #include "ui/gfx/geometry/size.h"
 
@@ -56,6 +57,9 @@ class CC_SURFACES_EXPORT Surface {
   void RunDrawCallbacks();
 
   base::WeakPtr<SurfaceFactory> factory() { return factory_; }
+  base::hash_set<SurfaceSequence>& destruction_dependencies() {
+    return destruction_dependencies_;
+  }
 
  private:
   void ClearCopyRequests();
@@ -66,6 +70,7 @@ class CC_SURFACES_EXPORT Surface {
   // TODO(jamesr): Support multiple frames in flight.
   scoped_ptr<CompositorFrame> current_frame_;
   int frame_index_;
+  base::hash_set<SurfaceSequence> destruction_dependencies_;

[piman, 2014/11/05 00:36:15]

Could this be a vector? AFAICT the only things that write into the set is the
RequireCallback that is only called with a new sequence, and the erase (so
you're guaranteed to have unique entries, you could DCHECK it even). It's only
read sequentially too.

 
   base::Closure draw_callback_;