Initial attempt at counting layers in the compositor thread.

cc/trees/layer_tree_host_impl.h

 // 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.
 
 #ifndef CC_TREES_LAYER_TREE_HOST_IMPL_H_
 #define CC_TREES_LAYER_TREE_HOST_IMPL_H_
 
 #include <list>
 #include <set>
 #include <string>
@@ skipping 446 matching lines @@
   // When a SwapPromiseMonitor is created on the impl thread, it calls
   // InsertSwapPromiseMonitor() to register itself with LayerTreeHostImpl.
   // When the monitor is destroyed, it calls RemoveSwapPromiseMonitor()
   // to unregister itself.
   void InsertSwapPromiseMonitor(SwapPromiseMonitor* monitor);
   void RemoveSwapPromiseMonitor(SwapPromiseMonitor* monitor);
 
   void RegisterPictureLayerImpl(PictureLayerImpl* layer);
   void UnregisterPictureLayerImpl(PictureLayerImpl* layer);
 
+  // Public only for for unit testing

[danakj, 2014/07/10 18:03:41]

comments are full sentences with periods

+  size_t num_layers_for_testing() { return num_layers_; }
+
  protected:
   LayerTreeHostImpl(
       const LayerTreeSettings& settings,
       LayerTreeHostImplClient* client,
       Proxy* proxy,
       RenderingStatsInstrumentation* rendering_stats_instrumentation,
       SharedBitmapManager* manager,
       int id);
 
   gfx::SizeF ComputeInnerViewportContainerSize() const;
@@ skipping 212 matching lines @@
 
   SharedBitmapManager* shared_bitmap_manager_;
   int id_;
 
   std::set<SwapPromiseMonitor*> swap_promise_monitor_;
 
   size_t transfer_buffer_memory_limit_;
 
   std::vector<PictureLayerImpl*> picture_layers_;
 
+  // The number of layers on the most recent frame,
+  // whether or not they were drawn.
+  // Default value is 0.
+  size_t num_layers_;

[dneto, 2014/07/10 01:29:03]

Not sure if size_t is appropriate here, or overkill.  I went with size_t because
the Chromium style guide says to use size_t when counting things. To be honest
unsigned would feel more natural.

[Ian Vollick, 2014/07/10 03:16:23]

I agree that this is overkill, but there's no harm in using a size_t for style's
sake. I think this is fine.

[danakj, 2014/07/10 18:03:41]

"unsigned" is generally banned. You'd use an int otherwise (we use unsigned for
GL data types actually, or uint32 but that's one of few exceptions).

[dneto, 2014/07/10 18:44:16]

Acknowledged.

[dneto, 2014/07/10 18:44:17]

Acknowledged.

+
   DISALLOW_COPY_AND_ASSIGN(LayerTreeHostImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_HOST_IMPL_H_