gpu: Empty swaps for surfaceless output surfaces.

components/display_compositor/buffer_queue.cc

 // Copyright 2014 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 "components/display_compositor/buffer_queue.h"
 
 #include "base/containers/adapters.h"
 #include "base/memory/ptr_util.h"
 #include "build/build_config.h"
 #include "components/display_compositor/gl_helper.h"
@@ skipping 165 matching lines @@
 
   new_surface->damage = surface->damage;
 
   // Copy the entire texture.
   CopyBufferDamage(new_surface->texture, surface->texture, gfx::Rect(),
                    gfx::Rect(size_));
   return new_surface;
 }
 
 void BufferQueue::PageFlipComplete() {
-  DCHECK(!in_flight_surfaces_.empty());
+  // Early out when no surface is in-flight. This can happen when using
+  // overlays and page flipping without changing the primary plane.
+  if (in_flight_surfaces_.empty())
+    return;
   if (displayed_surface_)
     available_surfaces_.push_back(std::move(displayed_surface_));
   displayed_surface_ = std::move(in_flight_surfaces_.front());
   in_flight_surfaces_.pop_front();
 }
 
+uint32_t BufferQueue::GetCurrentTextureId() const {
+  // Return current surface texture if bound.
+  if (current_surface_)
+    return current_surface_->texture;
+
+  // Return in-flight or displayed surface texture if no surface is
+  // currently bound. This can happen when using overlays and surface
+  // damage is empty.
+  if (!in_flight_surfaces_.empty())
+    return in_flight_surfaces_.back()->texture;
+  if (displayed_surface_)
+    return displayed_surface_->texture;
+
+  return 0;
+}
+
 void BufferQueue::FreeAllSurfaces() {
   displayed_surface_.reset();
   current_surface_.reset();
   // This is intentionally not emptied since the swap buffers acks are still
   // expected to arrive.
   for (auto& surface : in_flight_surfaces_)
     surface = nullptr;
   available_surfaces_.clear();
 }
 
@@ skipping 71 matching lines @@
       texture(texture),
       image(image),
       stencil(stencil),
       damage(rect) {}
 
 BufferQueue::AllocatedSurface::~AllocatedSurface() {
   buffer_queue->FreeSurfaceResources(this);
 }
 
 }  // namespace display_compositor