cc: Clear checker-image tracking on navigation and visibility changes.

cc/trees/layer_tree_host_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_host_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 1262 matching lines @@
     // becoming invisible in NotifyAllTileTasksComplete to avoid interrupting
     // running work.
     SetContextVisibility(true);
 
     // If |global_tile_state_.hard_memory_limit_in_bytes| is greater than 0, we
     // allow the image decode controller to retain resources. We handle the
     // equal to 0 case in NotifyAllTileTasksComplete to avoid interrupting
     // running work.
     if (image_decode_cache_)
       image_decode_cache_->SetShouldAggressivelyFreeResources(false);
+  } else {
+    // When the memory policy is set to zero, its important to release any
+    // decoded images cached by the tracker. But we can not re-checker any
+    // images that have been displayed since the resources, if held by the
+    // browser, may be re-used. Which is why its important to maintain the
+    // decode policy tracking.
+    bool can_clear_decode_policy_tracking = false;
+    tile_manager_.ClearCheckerImageTracking(can_clear_decode_policy_tracking);
   }
 
   DCHECK(resource_pool_);
   resource_pool_->CheckBusyResources();
   // Soft limit is used for resource pool such that memory returns to soft
   // limit after going over.
   resource_pool_->SetResourceUsageLimits(
       global_tile_state_.soft_memory_limit_in_bytes,
       global_tile_state_.num_resources_limit);
 
@@ skipping 1039 matching lines @@
 }
 
 std::vector<base::Closure>
 LayerTreeHostImpl::TakeCompletedImageDecodeCallbacks() {
   auto result = std::move(completed_image_decode_callbacks_);
   completed_image_decode_callbacks_.clear();
   return result;
 }
 
 void LayerTreeHostImpl::ClearImageCacheOnNavigation() {
+  // It is safe to clear the decode policy tracking on navigations since it
+  // comes with an invalidation and the image ids are never re-used.
+  bool can_clear_decode_policy_tracking = true;
+  tile_manager_.ClearCheckerImageTracking(can_clear_decode_policy_tracking);
   if (image_decode_cache_)
     image_decode_cache_->ClearCache();
 }
 
 void LayerTreeHostImpl::DidChangeScrollbarVisibility() {
   // Need a commit since input handling for scrollbars is handled in Blink so
   // we need to communicate to Blink when the compositor shows/hides the
   // scrollbars.
   client_->SetNeedsCommitOnImplThread();
 }
@@ skipping 1939 matching lines @@
 
 void LayerTreeHostImpl::ShowScrollbarsForImplScroll(ElementId element_id) {
   if (!element_id)
     return;
   if (ScrollbarAnimationController* animation_controller =
           ScrollbarAnimationControllerForElementId(element_id))
     animation_controller->DidScrollUpdate();
 }
 
 }  // namespace cc