Call OnSwapBuffersComplete at the end of each frame

cc/output/software_renderer.cc

Index: cc/output/software_renderer.cc
diff --git a/cc/output/software_renderer.cc b/cc/output/software_renderer.cc
index c53e0c7530ef3c37daab40237dac716b51182bfc..7d8453825433d71b14089489aad2a751efa2962a 100644
--- a/cc/output/software_renderer.cc
+++ b/cc/output/software_renderer.cc
@@ -68,7 +68,7 @@ SoftwareRenderer::SoftwareRenderer(RendererClient* client,
   // The updater can access bitmaps while the SoftwareRenderer is using them.
   capabilities_.allow_partial_texture_updates = true;
   capabilities_.using_partial_swap = true;
-  if (Settings().compositor_frame_message && client_->HasImplThread())
+  if (client_->HasImplThread())
     capabilities_.using_swap_complete_callback = true;
   compositor_frame_.software_frame_data.reset(new SoftwareFrameData());
 }
@@ -107,8 +107,11 @@ void SoftwareRenderer::FinishDrawingFrame(DrawingFrame* frame) {
 }
 
 void SoftwareRenderer::SwapBuffers(const ui::LatencyInfo& latency_info) {
-  if (Settings().compositor_frame_message)
+  if (Settings().compositor_frame_message) {
     output_surface_->SendFrameToParentCompositor(&compositor_frame_);
+  } else {
+    output_surface_->SwapBuffers(latency_info);
+  }
 }
 
 void SoftwareRenderer::ReceiveCompositorFrameAck(