cc: Reject CompositorFrames to old child surfaces

cc/surfaces/surface.cc

Index: cc/surfaces/surface.cc
diff --git a/cc/surfaces/surface.cc b/cc/surfaces/surface.cc
index 6dc261bde664d9549a95c85dfc905caffe12ec65..f78800d8b2637ce07725bec20ae58a70fae43d8e 100644
--- a/cc/surfaces/surface.cc
+++ b/cc/surfaces/surface.cc
@@ -15,7 +15,9 @@
 #include "cc/surfaces/local_surface_id_allocator.h"
 #include "cc/surfaces/pending_frame_observer.h"
 #include "cc/surfaces/surface_factory.h"
+#include "cc/surfaces/surface_factory_client.h"
 #include "cc/surfaces/surface_manager.h"
+#include "cc/surfaces/surface_resource_holder_client.h"
 
 namespace cc {
 
@@ -50,9 +52,23 @@ void Surface::SetPreviousFrameSurface(Surface* surface) {
   surface->TakeLatencyInfoFromPendingFrame(&frame.metadata.latency_info);
 }
 
+void Surface::Close() {
+  closed_ = true;
+}
+
 void Surface::QueueFrame(CompositorFrame frame,
                          const DrawCallback& callback,
                          const WillDrawCallback& will_draw_callback) {
+  if (closed_) {
+    if (factory_ && factory_->resource_holder_client()) {
+      ReturnedResourceArray resources;
+      TransferableResource::ReturnResources(frame.resource_list, &resources);
+      factory_->resource_holder_client()->ReturnResources(resources);
+    }
+    callback.Run();
+    return;
+  }
+
   TakeLatencyInfoFromPendingFrame(&frame.metadata.latency_info);
 
   base::Optional<FrameData> previous_pending_frame_data =
@@ -68,6 +84,24 @@ void Surface::QueueFrame(CompositorFrame frame,
   bool is_pending_frame = !blocking_surfaces_.empty();
 
   if (is_pending_frame) {
+    // Reject CompositorFrames submitted to surfaces referenced from this
+    // CompositorFrame as fallbacks. This saves some CPU cycles to allow
+    // children to catch up to the parent.
+    base::flat_set<FrameSinkId> frame_sink_ids_for_dependencies;
+    for (const SurfaceId& surface_id : frame.metadata.activation_dependencies)
+      frame_sink_ids_for_dependencies.insert(surface_id.frame_sink_id());
+    for (const SurfaceId& surface_id : frame.metadata.referenced_surfaces) {
+      // If this |surface_id| corresponds to a fallback surface referenced by

[danakj, 2017/05/05 18:06:08]

This comment just says what the code below does, which does not add anything for
me. What I'd like is a comment explaining why a surface being in both
activation_dependencies and in referenced_surfaces means it is a fallback
surface.

[Fady Samuel, 2017/05/05 18:55:11]

I've improved the comment, hopefully.

+      // this CompositorFrame, then we close the corresponding surface to avoid
+      // accepting new frames.
+      bool is_fallback_surface =
+          frame_sink_ids_for_dependencies.count(surface_id.frame_sink_id()) > 0;
+      if (is_fallback_surface) {
+        Surface* surface = factory_->manager()->GetSurfaceForId(surface_id);
+        DCHECK(surface);
+        surface->Close();
+      }
+    }
     pending_frame_data_ =
         FrameData(std::move(frame), callback, will_draw_callback);
     // Ask the surface manager to inform |this| when its dependencies are