Surface Synchronization: Distinguish between dependencies and references

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index 62654865f4d51e641bd820b3652b2b945f2c1adc..a7d1488d276a0b500afbb2edfbef2e93b1dd9c74 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -1624,13 +1624,14 @@ CompositorFrameMetadata LayerTreeHostImpl::MakeCompositorFrameMetadata() const {
   for (LayerImpl* surface_layer : active_tree_->SurfaceLayers()) {
     SurfaceLayerImpl* surface_layer_impl =
         static_cast<SurfaceLayerImpl*>(surface_layer);
-    metadata.referenced_surfaces.push_back(
-        surface_layer_impl->primary_surface_info().id());
-    // We need to retain a reference to the fallback surface too so that it's
-    // guaranteed to be available when needed.
-    if (surface_layer_impl->fallback_surface_info().is_valid()) {
+    if (!settings_.enable_surface_synchronization) {

[vmpstr, 2017/04/11 18:35:17]

nit: can you flip this to the positive and exchange if/else blocks

[Fady Samuel, 2017/04/11 19:39:24]

Done.

       metadata.referenced_surfaces.push_back(
-          surface_layer_impl->fallback_surface_info().id());
+          surface_layer_impl->primary_surface_info().id());
+    } else {
+      if (surface_layer_impl->fallback_surface_info().is_valid()) {
+        metadata.referenced_surfaces.push_back(
+            surface_layer_impl->fallback_surface_info().id());

[vmpstr, 2017/04/11 18:35:17]

hmm why do we not reference primary surface info if we have surface
synchronization enabled?

[Fady Samuel, 2017/04/11 19:39:24]

As the description says, fallbacks are references and primaries are
dependencies. Dependencies eventually become references when the CompositorFrame
activates AND the parent refers to the child in a fallback.

+      }
     }
   }
   if (!InnerViewportScrollLayer())