Fixes black flash when accelerated composited paints the tab background

content/browser/renderer_host/render_widget_host_view_aura.cc

 // Copyright (c) 2012 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 "content/browser/renderer_host/render_widget_host_view_aura.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
@@ skipping 200 matching lines @@
       is_fullscreen_(false),
       popup_parent_host_view_(NULL),
       popup_child_host_view_(NULL),
       is_loading_(false),
       text_input_type_(ui::TEXT_INPUT_TYPE_NONE),
       can_compose_inline_(true),
       has_composition_text_(false),
       current_surface_(0),
       paint_canvas_(NULL),
       synthetic_move_sent_(false),
-      needs_update_texture_(false) {
+      accelerated_compositing_state_changed_(false) {
   host_->SetView(this);
   window_observer_.reset(new WindowObserver(this));
   window_->AddObserver(window_observer_.get());
   aura::client::SetTooltipText(window_, &tooltip_);
   aura::client::SetActivationDelegate(window_, this);
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 // RenderWidgetHostViewAura, RenderWidgetHostView implementation:
 
@@ skipping 140 matching lines @@
     const std::vector<gfx::Rect>& character_bounds) {
   composition_character_bounds_ = character_bounds;
 }
 
 void RenderWidgetHostViewAura::DidUpdateBackingStore(
     const gfx::Rect& scroll_rect, int scroll_dx, int scroll_dy,
     const std::vector<gfx::Rect>& copy_rects) {
   if (!window_->IsVisible())
     return;
 
-  if (needs_update_texture_)
+  if (accelerated_compositing_state_changed_)
     UpdateExternalTexture();
 
   gfx::Rect clip_rect;
   if (paint_canvas_) {
     SkRect sk_clip_rect;
     if (paint_canvas_->sk_canvas()->getClipBounds(&sk_clip_rect))
       clip_rect = gfx::SkRectToRect(sk_clip_rect);
   }
 
   if (!scroll_rect.IsEmpty())
@@ skipping 77 matching lines @@
       output->getTopDevice()->accessBitmap(true).getPixels());
   scoped_callback_runner.Release();
   gl_helper->CopyTextureTo(container->texture_id(),
                            container->size(),
                            size_in_pixel,
                            addr,
                            callback);
 }
 
 void RenderWidgetHostViewAura::OnAcceleratedCompositingStateChange() {
-  // Delay UpdateExternalTexture until we actually got a software frame.
+  // Delay processing the state change until we either get a software frame if
+  // switching to software mode or receive a buffers swapped notification
+  // if switching to accelerated mode.
   // Sometimes (e.g. on a page load) the renderer will spuriously disable then
   // re-enable accelerated compositing, causing us to flash.
   // TODO(piman): factor the enable/disable accelerated compositing message into
   // the UpdateRect/AcceleratedSurfaceBuffersSwapped messages so that we have
   // fewer inconsistent temporary states.
-  needs_update_texture_ = true;
-
-  // Don't scale the contents in accelerated mode because the renderer takes
-  // care of it.
-  window_->layer()->set_scale_content(
-      !host_->is_accelerated_compositing_active());
+  accelerated_compositing_state_changed_ = true;
 }
 
 void RenderWidgetHostViewAura::UpdateExternalTexture() {
-  needs_update_texture_ = false;
+  // Delay processing accelerated compositing state change till here where we
+  // act upon the state change. (Clear the external texture if switching to
+  // software mode or set the external texture if going to accelerated mode).
+  if (accelerated_compositing_state_changed_) {
+    // Don't scale the contents in accelerated mode because the renderer takes
+    // care of it.
+    window_->layer()->set_scale_content(
+        !host_->is_accelerated_compositing_active());
+
+    accelerated_compositing_state_changed_ = false;
+  }
+
   if (current_surface_ != 0 &&
       host_->is_accelerated_compositing_active()) {
     ImageTransportClient* container =
         image_transport_clients_[current_surface_];
     if (container)
       container->Update();
     window_->SetExternalTexture(container);
 
     released_front_lock_ = NULL;
 
@@ skipping 907 matching lines @@
 RenderWidgetHostView* RenderWidgetHostView::CreateViewForWidget(
     RenderWidgetHost* widget) {
   return new RenderWidgetHostViewAura(widget);
 }
 
 // static
 void content::RenderWidgetHostViewPort::GetDefaultScreenInfo(
     WebKit::WebScreenInfo* results) {
   GetScreenInfoForWindow(results, NULL);
 }