Respect window transparency when applying window shape.

ui/compositor/layer.cc

 // Copyright (c) 2012 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 "ui/compositor/layer.h"
 
 #include <algorithm>
 
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
@@ skipping 360 matching lines @@
     filters.Append(cc::FilterOperation::CreateInvertFilter(1.0));
   // Brightness goes last, because the resulting colors neeed clamping, which
   // cause further color matrix filters to be applied separately. In this order,
   // they all can be combined in a single pass.
   if (layer_brightness_) {
     filters.Append(cc::FilterOperation::CreateSaturatingBrightnessFilter(
         layer_brightness_));
   }
   if (alpha_shape_) {
     filters.Append(cc::FilterOperation::CreateAlphaThresholdFilter(
-            *alpha_shape_, 1.f, 0.f));
+            *alpha_shape_, 0.f, 0.f));
   }
 
   cc_layer_->SetFilters(filters);
 }
 
 void Layer::SetLayerBackgroundFilters() {
   cc::FilterOperations filters;
   if (zoom_ != 1)
     filters.Append(cc::FilterOperation::CreateZoomFilter(zoom_, zoom_inset_));
 
@@ skipping 636 matching lines @@
       children_.end(),
       std::bind2nd(std::mem_fun(&Layer::RemoveAnimatorsInTreeFromCollection),
                    collection));
 }
 
 bool Layer::IsAnimating() const {
   return animator_ && animator_->is_animating();
 }
 
 }  // namespace ui