FrameGenerator: Don't issue BeginFrames if we have nothing to draw

services/ui/ws/frame_generator.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "services/ui/ws/frame_generator.h"
 
 #include <utility>
 #include <vector>
 
 #include "base/containers/adapters.h"
@@ skipping 25 matching lines @@
       widget, std::move(sink_request), binding_.CreateInterfacePtrAndBind(),
       std::move(display_request));
 }
 
 FrameGenerator::~FrameGenerator() = default;
 
 void FrameGenerator::SetDeviceScaleFactor(float device_scale_factor) {
   if (device_scale_factor_ == device_scale_factor)
     return;
   device_scale_factor_ = device_scale_factor;
-  compositor_frame_sink_->SetNeedsBeginFrame(true);
+  if (window_manager_surface_info_.id().is_valid())
+    compositor_frame_sink_->SetNeedsBeginFrame(true);
 }
 
 void FrameGenerator::OnSurfaceCreated(const cc::SurfaceInfo& surface_info) {
   DCHECK(surface_info.id().is_valid());
 
   // Only handle embedded surfaces changing here. The display root surface
   // changing is handled immediately after the CompositorFrame is submitted.
   if (surface_info != window_manager_surface_info_) {
     window_manager_surface_info_ = surface_info;
     compositor_frame_sink_->SetNeedsBeginFrame(true);
@@ skipping 110 matching lines @@
   auto* quad = pass->CreateAndAppendDrawQuad<cc::SurfaceDrawQuad>();
   quad->SetAll(sqs, bounds_at_origin /* rect */, gfx::Rect() /* opaque_rect */,
                bounds_at_origin /* visible_rect */, true /* needs_blending*/,
                window_manager_surface_info_.id(),
                cc::SurfaceDrawQuadType::PRIMARY, nullptr);
 }
 
 }  // namespace ws
 
 }  // namespace ui