Discard compositor frames from unloaded web content

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 <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 55 matching lines @@
       last_scrolled_layer_id_(Layer::INVALID_ID),
       overscroll_elasticity_layer_id_(Layer::INVALID_ID),
       page_scale_layer_id_(Layer::INVALID_ID),
       inner_viewport_scroll_layer_id_(Layer::INVALID_ID),
       outer_viewport_scroll_layer_id_(Layer::INVALID_ID),
       page_scale_factor_(page_scale_factor),
       min_page_scale_factor_(0),
       max_page_scale_factor_(0),
       device_scale_factor_(1.f),
       painted_device_scale_factor_(1.f),
+      content_source_id_(0),
       elastic_overscroll_(elastic_overscroll),
       layers_(new OwnedLayerImplList),
       viewport_size_invalid_(false),
       needs_update_draw_properties_(true),
       needs_full_tree_sync_(true),
       next_activation_forces_redraw_(false),
       has_ever_been_drawn_(false),
       handle_visibility_changed_(false),
       have_scroll_event_handlers_(false),
       event_listener_properties_(),
@@ skipping 377 matching lines @@
 
   // Active tree already shares the page_scale_factor object with pending
   // tree so only the limits need to be provided.
   target_tree->PushPageScaleFactorAndLimits(nullptr, min_page_scale_factor(),
                                             max_page_scale_factor());
   target_tree->SetDeviceScaleFactor(device_scale_factor());
   target_tree->set_painted_device_scale_factor(painted_device_scale_factor());
   target_tree->SetDeviceColorSpace(device_color_space_);
   target_tree->elastic_overscroll()->PushPendingToActive();
 
+  target_tree->set_content_source_id(content_source_id());
+
   target_tree->pending_page_scale_animation_ =
       std::move(pending_page_scale_animation_);
 
   target_tree->SetViewportLayersFromIds(
       overscroll_elasticity_layer_id_, page_scale_layer_id_,
       inner_viewport_scroll_layer_id_, outer_viewport_scroll_layer_id_);
 
   target_tree->RegisterSelection(selection_);
 
   // This should match the property synchronization in
@@ skipping 1635 matching lines @@
 
 void LayerTreeImpl::ResetAllChangeTracking() {
   layers_that_should_push_properties_.clear();
   // Iterate over all layers, including masks.
   for (auto& layer : *layers_)
     layer->ResetChangeTracking();
   property_trees_.ResetAllChangeTracking();
 }
 
 }  // namespace cc