Fix race conditions in window snapshot code.

cc/trees/layer_tree_impl.cc

 // Copyright 2011 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 "cc/trees/layer_tree_impl.h"
 
 #include "base/debug/trace_event.h"
 #include "cc/animation/keyframed_animation_curve.h"
 #include "cc/animation/scrollbar_animation_controller.h"
 #include "cc/debug/traced_value.h"
@@ skipping 22 matching lines @@
       outer_viewport_scroll_layer_(NULL),
       page_scale_factor_(1),
       page_scale_delta_(1),
       sent_page_scale_delta_(1),
       min_page_scale_factor_(0),
       max_page_scale_factor_(0),
       scrolling_layer_id_from_previous_tree_(0),
       contents_textures_purged_(false),
       viewport_size_invalid_(false),
       needs_update_draw_properties_(true),
-      needs_full_tree_sync_(true) {
+      needs_full_tree_sync_(true),
+      next_activation_forces_redraw_(false) {
 }
 
 LayerTreeImpl::~LayerTreeImpl() {
   // Need to explicitly clear the tree prior to destroying this so that
   // the LayerTreeImpl pointer is still valid in the LayerImpl dtor.
   root_layer_.reset();
 }
 
 static LayerImpl* FindRootScrollLayerRecursive(LayerImpl* layer) {
   if (!layer)
@@ skipping 50 matching lines @@
 
   render_surface_layer_list_.clear();
   set_needs_update_draw_properties();
   return root_layer_.Pass();
 }
 
 void LayerTreeImpl::PushPropertiesTo(LayerTreeImpl* target_tree) {
   // The request queue should have been processed and does not require a push.
   DCHECK_EQ(ui_resource_request_queue_.size(), 0u);
 
+  if (next_activation_forces_redraw_) {
+    layer_tree_host_impl_->SetFullRootLayerDamage();
+    next_activation_forces_redraw_ = false;
+  }
+
   target_tree->SetLatencyInfo(latency_info_);
   latency_info_.Clear();
   target_tree->SetPageScaleFactorAndLimits(
       page_scale_factor(), min_page_scale_factor(), max_page_scale_factor());
   target_tree->SetPageScaleDelta(
       target_tree->page_scale_delta() / target_tree->sent_page_scale_delta());
   target_tree->set_sent_page_scale_delta(1);
 
   if (settings().use_pinch_virtual_viewport) {
     target_tree->SetViewportLayersFromIds(
@@ skipping 579 matching lines @@
 const std::vector<LayerImpl*> LayerTreeImpl::LayersWithCopyOutputRequest()
     const {
   // Only the active tree needs to know about layers with copy requests, as
   // they are aborted if not serviced during draw.
   DCHECK(IsActiveTree());
 
   return layers_with_copy_output_request_;
 }
 
 }  // namespace cc