Make cc::CompositorFrames movable [Part 2 of 2]

cc/surfaces/surface_aggregator.cc

Index: cc/surfaces/surface_aggregator.cc
diff --git a/cc/surfaces/surface_aggregator.cc b/cc/surfaces/surface_aggregator.cc
index 066ffc8adb902fb4f194d3c9fae5ae64c64d6a16..0de6f290bce57d70ac94dc26cdd544d15a68375a 100644
--- a/cc/surfaces/surface_aggregator.cc
+++ b/cc/surfaces/surface_aggregator.cc
@@ -770,23 +770,20 @@ void SurfaceAggregator::PropagateCopyRequestPasses() {
   }
 }
 
-std::unique_ptr<CompositorFrame> SurfaceAggregator::Aggregate(
-    SurfaceId surface_id) {
+CompositorFrame SurfaceAggregator::Aggregate(SurfaceId surface_id) {
   Surface* surface = manager_->GetSurfaceForId(surface_id);
   DCHECK(surface);
   contained_surfaces_[surface_id] = surface->frame_index();
   const CompositorFrame* root_surface_frame = surface->GetEligibleFrame();
-  if (!root_surface_frame)
-    return nullptr;
+  if (!root_surface_frame->delegated_frame_data)
+    return CompositorFrame();
   TRACE_EVENT0("cc", "SurfaceAggregator::Aggregate");
 
-  std::unique_ptr<CompositorFrame> frame(new CompositorFrame);
-  frame->delegated_frame_data = base::WrapUnique(new DelegatedFrameData);
-
-  DCHECK(root_surface_frame->delegated_frame_data);
+  CompositorFrame frame;
+  frame.delegated_frame_data = base::WrapUnique(new DelegatedFrameData);
 
-  dest_resource_list_ = &frame->delegated_frame_data->resource_list;
-  dest_pass_list_ = &frame->delegated_frame_data->render_pass_list;
+  dest_resource_list_ = &frame.delegated_frame_data->resource_list;
+  dest_pass_list_ = &frame.delegated_frame_data->render_pass_list;
 
   valid_surfaces_.clear();
   PrewalkResult prewalk_result;
@@ -807,7 +804,7 @@ std::unique_ptr<CompositorFrame> SurfaceAggregator::Aggregate(
   DCHECK(referenced_surfaces_.empty());
 
   if (dest_pass_list_->empty())
-    return nullptr;
+    return CompositorFrame();
 
   dest_pass_list_ = NULL;
   ProcessAddedAndRemovedSurfaces();
@@ -819,7 +816,7 @@ std::unique_ptr<CompositorFrame> SurfaceAggregator::Aggregate(
        ++it) {
     Surface* surface = manager_->GetSurfaceForId(it->first);
     if (surface)
-      surface->TakeLatencyInfo(&frame->metadata.latency_info);
+      surface->TakeLatencyInfo(&frame.metadata.latency_info);
   }
 
   // TODO(jamesr): Aggregate all resource references into the returned frame's