Refactor client visibility handling

cc/trees/layer_tree_host_impl.h

Index: cc/trees/layer_tree_host_impl.h
diff --git a/cc/trees/layer_tree_host_impl.h b/cc/trees/layer_tree_host_impl.h
index 6af8dd9f00fc8e75b34a4f4b0f68ad32a8dcf950..78b087b7770557200bed4734f652af9c7c8b867b 100644
--- a/cc/trees/layer_tree_host_impl.h
+++ b/cc/trees/layer_tree_host_impl.h
@@ -27,6 +27,7 @@
 #include "cc/layers/layer_collections.h"
 #include "cc/layers/render_pass_sink.h"
 #include "cc/output/begin_frame_args.h"
+#include "cc/output/context_cache_controller.h"
 #include "cc/output/delegating_renderer.h"
 #include "cc/output/managed_memory_policy.h"
 #include "cc/output/output_surface_client.h"
@@ -712,6 +713,9 @@ class CC_EXPORT LayerTreeHostImpl
   bool ScrollAnimationUpdateTarget(ScrollNode* scroll_node,
                                    const gfx::Vector2dF& scroll_delta);
 
+  void SetMainContextVisibility(bool is_visible);
+  void SetWorkerContextVisibility(bool is_visible);
+
   using UIResourceMap = std::unordered_map<UIResourceId, UIResourceData>;
   UIResourceMap ui_resource_map_;
 
@@ -722,6 +726,14 @@ class CC_EXPORT LayerTreeHostImpl
 
   OutputSurface* output_surface_;
 
+  // The following scoped variables must not outlive the |output_surface_|.
+  // These should be transfered to ContextCacheController's
+  // ClientBecameNotVisible() before the output surface is destroyed.
+  std::unique_ptr<ContextCacheController::ScopedVisibility>
+      main_context_visibility_;
+  std::unique_ptr<ContextCacheController::ScopedVisibility>
+      worker_context_visibility_;
+
   std::unique_ptr<ResourceProvider> resource_provider_;
   bool need_update_gpu_rasterization_status_;
   bool content_is_suitable_for_gpu_rasterization_;