cc: Toward merging DrawFrame and SwapBuffers in DelegatingRenderer.

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 f46d3cddfba829d2c71428b1f699eddaea703af4..8ed36a9373411cf815fe84fbffdbe2227d114e71 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -1723,24 +1723,6 @@ void LayerTreeHostImpl::DrawLayers(FrameData* frame) {
   renderer_->DrawFrame(&frame->render_passes);
   // The render passes should be consumed by the renderer.
   DCHECK(frame->render_passes.empty());
-
-  // The next frame should start by assuming nothing has changed, and changes
-  // are noted as they occur.
-  // TODO(boliu): If we did a temporary software renderer frame, propogate the
-  // damage forward to the next frame.
-  for (size_t i = 0; i < frame->render_surface_layer_list->size(); i++) {
-    (*frame->render_surface_layer_list)[i]
-        ->render_surface()
-        ->damage_tracker()
-        ->DidDrawDamagedArea();
-  }
-  active_tree_->ResetAllChangeTracking();
-
-  active_tree_->set_has_ever_been_drawn(true);
-  devtools_instrumentation::DidDrawFrame(id_);
-  benchmark_instrumentation::IssueImplThreadRenderingStatsEvent(
-      rendering_stats_instrumentation_->impl_thread_rendering_stats());
-  rendering_stats_instrumentation_->AccumulateAndClearImplThreadStats();
 }
 
 void LayerTreeHostImpl::DidDrawAllLayers(const FrameData& frame) {
@@ -1881,28 +1863,48 @@ void LayerTreeHostImpl::UpdateTreeResourcesForGpuRasterizationIfNeeded() {
 
 bool LayerTreeHostImpl::SwapBuffers(const LayerTreeHostImpl::FrameData& frame) {
   ResetRequiresHighResToDraw();
+  bool swapped = false;
   if (frame.has_no_damage) {
     active_tree()->BreakSwapPromises(SwapPromise::SWAP_FAILS);
-    return false;
-  }
-  CompositorFrameMetadata metadata = MakeCompositorFrameMetadata();
-  metadata.may_contain_video = frame.may_contain_video;
-  active_tree()->FinishSwapPromises(&metadata);
-  for (auto& latency : metadata.latency_info) {
-    TRACE_EVENT_WITH_FLOW1("input,benchmark", "LatencyInfo.Flow",
-                           TRACE_ID_DONT_MANGLE(latency.trace_id()),
-                           TRACE_EVENT_FLAG_FLOW_IN | TRACE_EVENT_FLAG_FLOW_OUT,
-                           "step", "SwapBuffers");
-    // Only add the latency component once for renderer swap, not the browser
-    // swap.
-    if (!latency.FindLatency(ui::INPUT_EVENT_LATENCY_RENDERER_SWAP_COMPONENT, 0,
-                             nullptr)) {
-      latency.AddLatencyNumber(ui::INPUT_EVENT_LATENCY_RENDERER_SWAP_COMPONENT,
-                               0, 0);
+  } else {
+    CompositorFrameMetadata metadata = MakeCompositorFrameMetadata();
+    metadata.may_contain_video = frame.may_contain_video;
+    active_tree()->FinishSwapPromises(&metadata);
+    for (auto& latency : metadata.latency_info) {
+      TRACE_EVENT_WITH_FLOW1(
+          "input,benchmark", "LatencyInfo.Flow",
+          TRACE_ID_DONT_MANGLE(latency.trace_id()),
+          TRACE_EVENT_FLAG_FLOW_IN | TRACE_EVENT_FLAG_FLOW_OUT, "step",
+          "SwapBuffers");
+      // Only add the latency component once for renderer swap, not the browser
+      // swap.
+      if (!latency.FindLatency(ui::INPUT_EVENT_LATENCY_RENDERER_SWAP_COMPONENT,
+                               0, nullptr)) {
+        latency.AddLatencyNumber(
+            ui::INPUT_EVENT_LATENCY_RENDERER_SWAP_COMPONENT, 0, 0);
+      }
     }
+    renderer_->SwapBuffers(std::move(metadata));
+    swapped = true;
   }
-  renderer_->SwapBuffers(std::move(metadata));
-  return true;
+
+  // The next frame should start by assuming nothing has changed, and changes

[danakj, 2016/09/07 00:25:35]

I think this stuff shouldn't actually happen if has_no_damage, it didn't in
DrawLayers, will fix.

[danakj, 2016/09/07 00:32:15]

Fixed.

+  // are noted as they occur.
+  // TODO(boliu): If we did a temporary software renderer frame, propogate the
+  // damage forward to the next frame.
+  for (size_t i = 0; i < frame.render_surface_layer_list->size(); i++) {
+    auto* surface = (*frame.render_surface_layer_list)[i]->render_surface();
+    surface->damage_tracker()->DidDrawDamagedArea();
+  }
+  active_tree_->ResetAllChangeTracking();
+
+  active_tree_->set_has_ever_been_drawn(true);
+  devtools_instrumentation::DidDrawFrame(id_);
+  benchmark_instrumentation::IssueImplThreadRenderingStatsEvent(
+      rendering_stats_instrumentation_->impl_thread_rendering_stats());
+  rendering_stats_instrumentation_->AccumulateAndClearImplThreadStats();
+
+  return swapped;
 }
 
 void LayerTreeHostImpl::WillBeginImplFrame(const BeginFrameArgs& args) {