Add support for tagging layers.

cc/layer_tree_host.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/layer_tree_host.h"
 
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
 #include "base/message_loop.h"
 #include "base/stl_util.h"
@@ skipping 882 matching lines @@
                 layer->notifyAnimationStarted(events[eventIndex], wallClockTime.ToDoubleT());
             else
                 layer->notifyAnimationFinished(wallClockTime.ToDoubleT());
         }
     }
 
     for (size_t childIndex = 0; childIndex < layer->children().size(); ++childIndex)
         setAnimationEventsRecursive(events, layer->children()[childIndex].get(), wallClockTime);
 }
 
+Layer* LayerTreeHost::getFirstLayerWithTags(unsigned int tags) const
+{
+    std::queue<Layer*> layers;
+    layers.push(m_rootLayer.get());
+
+    while (!layers.empty()) {
+        Layer* layer = layers.front();
+        layers.pop();
+
+        if (!layer)
+            return NULL;
+
+        if (layer->getTags() & tags)
+            return layer;
+
+        for (LayerList::const_iterator it = layer->children().begin();
+             it != layer->children().end(); ++it) {
+            layers.push(it->get());
+        }
+    }
+
+    return NULL;
+}
+
 }  // namespace cc