Add DisplayCompositorTest.

services/ui/surfaces/display_compositor.cc

Index: services/ui/surfaces/display_compositor.cc
diff --git a/services/ui/surfaces/display_compositor.cc b/services/ui/surfaces/display_compositor.cc
index bb27998d8480fddfd95da63a6e6b760b70f2a2ca..cfe1e5157663b14c2e8896813683f9e4d515f1c4 100644
--- a/services/ui/surfaces/display_compositor.cc
+++ b/services/ui/surfaces/display_compositor.cc
@@ -10,7 +10,9 @@ namespace ui {
 
 DisplayCompositor::DisplayCompositor(
     cc::mojom::DisplayCompositorClientPtr client)
-    : client_(std::move(client)) {
+    : client_(std::move(client)),
+      reference_manager_(&manager_),
+      root_surface_id_(reference_manager_->GetRootSurfaceId()) {
   manager_.AddObserver(this);
 }
 
@@ -25,7 +27,7 @@ void DisplayCompositor::AddSurfaceReference(const cc::SurfaceId& parent_id,
   // If there are no temporary references for the FrameSinkId then we can just
   // add reference and return.
   if (vector_iter == temp_references_.end()) {
-    manager_.AddSurfaceReference(parent_id, child_id);
+    reference_manager_->AddSurfaceReference(parent_id, child_id);
     return;
   }
 
@@ -37,16 +39,16 @@ void DisplayCompositor::AddSurfaceReference(const cc::SurfaceId& parent_id,
       std::find(refs.begin(), refs.end(), child_id.local_frame_id());
 
   if (temp_ref_iter == refs.end()) {
-    manager_.AddSurfaceReference(parent_id, child_id);
+    reference_manager_->AddSurfaceReference(parent_id, child_id);
     return;
   }
 
   // All surfaces get a temporary reference to the top level root. If we want to
   // add a real reference to the top level root then we do nothing. Otherwise
   // remove the temporary reference and add the real reference.
-  if (parent_id != manager_.GetRootSurfaceId()) {
-    manager_.AddSurfaceReference(parent_id, child_id);
-    manager_.RemoveSurfaceReference(manager_.GetRootSurfaceId(), child_id);
+  if (parent_id != root_surface_id_) {
+    reference_manager_->AddSurfaceReference(parent_id, child_id);
+    reference_manager_->RemoveSurfaceReference(root_surface_id_, child_id);
   }
 
   // Remove temporary references for surfaces with the same FrameSinkId that
@@ -55,7 +57,7 @@ void DisplayCompositor::AddSurfaceReference(const cc::SurfaceId& parent_id,
   // parent doesn't need them anymore.
   for (auto iter = refs.begin(); iter != temp_ref_iter; ++iter) {
     cc::SurfaceId id = cc::SurfaceId(child_id.frame_sink_id(), *iter);
-    manager_.RemoveSurfaceReference(manager_.GetRootSurfaceId(), id);
+    reference_manager_->RemoveSurfaceReference(root_surface_id_, id);
   }
 
   // Remove markers for temporary references up to |child_id|, as the temporary
@@ -70,14 +72,14 @@ void DisplayCompositor::AddSurfaceReference(const cc::SurfaceId& parent_id,
 
 void DisplayCompositor::RemoveRootSurfaceReference(
     const cc::SurfaceId& child_id) {
-  RemoveSurfaceReference(manager_.GetRootSurfaceId(), child_id);
+  RemoveSurfaceReference(root_surface_id_, child_id);
 }
 
 void DisplayCompositor::RemoveSurfaceReference(const cc::SurfaceId& parent_id,
                                                const cc::SurfaceId& child_id) {
   // TODO(kylechar): Each remove reference can trigger GC, it would be better if
   // we GC only once if removing multiple references.
-  manager_.RemoveSurfaceReference(parent_id, child_id);
+  reference_manager_->RemoveSurfaceReference(parent_id, child_id);
 }
 
 DisplayCompositor::~DisplayCompositor() {
@@ -85,9 +87,8 @@ DisplayCompositor::~DisplayCompositor() {
   for (auto& map_entry : temp_references_) {
     const cc::FrameSinkId& frame_sink_id = map_entry.first;
     for (auto& local_frame_id : map_entry.second) {
-      manager_.RemoveSurfaceReference(
-          manager_.GetRootSurfaceId(),
-          cc::SurfaceId(frame_sink_id, local_frame_id));
+      reference_manager_->RemoveSurfaceReference(
+          root_surface_id_, cc::SurfaceId(frame_sink_id, local_frame_id));
     }
   }
   manager_.RemoveObserver(this);
@@ -102,7 +103,7 @@ void DisplayCompositor::OnSurfaceCreated(const cc::SurfaceId& surface_id,
   // the first will be destroyed and then if there are no references it will be
   // deleted during surface GC. A temporary reference, removed when a real
   // reference is received, is added to prevent this from happening.
-  manager_.AddSurfaceReference(manager_.GetRootSurfaceId(), surface_id);
+  reference_manager_->AddSurfaceReference(root_surface_id_, surface_id);
   temp_references_[surface_id.frame_sink_id()].push_back(
       surface_id.local_frame_id());