cc: Remove some DCHECKs in CopyOutputRequest code.

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 "base/debug/trace_event.h"
 #include "cc/animation/keyframed_animation_curve.h"
 #include "cc/animation/scrollbar_animation_controller.h"
 #include "cc/debug/traced_value.h"
@@ skipping 547 matching lines @@
 
 void LayerTreeImpl::WillModifyTilePriorities() {
   layer_tree_host_impl_->SetNeedsManageTiles();
 }
 
 void LayerTreeImpl::AddLayerWithCopyOutputRequest(LayerImpl* layer) {
   // Only the active tree needs to know about layers with copy requests, as
   // they are aborted if not serviced during draw.
   DCHECK(IsActiveTree());
 
-  DCHECK(std::find(layers_with_copy_output_request_.begin(),
-                   layers_with_copy_output_request_.end(),
-                   layer) == layers_with_copy_output_request_.end());
+  if (std::find(layers_with_copy_output_request_.begin(),
+                layers_with_copy_output_request_.end(),
+                layer) != layers_with_copy_output_request_.end())
+    return;
   layers_with_copy_output_request_.push_back(layer);
 }
 
 void LayerTreeImpl::RemoveLayerWithCopyOutputRequest(LayerImpl* layer) {
   // Only the active tree needs to know about layers with copy requests, as
   // they are aborted if not serviced during draw.
   DCHECK(IsActiveTree());
 
   std::vector<LayerImpl*>::iterator it = std::find(
       layers_with_copy_output_request_.begin(),
       layers_with_copy_output_request_.end(),
       layer);
   DCHECK(it != layers_with_copy_output_request_.end());
   if (it != layers_with_copy_output_request_.end())
     layers_with_copy_output_request_.erase(it);
 }
 
 const std::vector<LayerImpl*> LayerTreeImpl::LayersWithCopyOutputRequest()
     const {
   // Only the active tree needs to know about layers with copy requests, as
   // they are aborted if not serviced during draw.
   DCHECK(IsActiveTree());
 
   return layers_with_copy_output_request_;
 }
 
 }  // namespace cc