cc: Allow changing mask type when pushing properties.

cc/layers/picture_layer_impl.cc

 // Copyright 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 "cc/layers/picture_layer_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 102 matching lines @@
       is_directly_composited_image_(false) {
   layer_tree_impl()->RegisterPictureLayerImpl(this);
 }
 
 PictureLayerImpl::~PictureLayerImpl() {
   if (twin_layer_)
     twin_layer_->twin_layer_ = nullptr;
   layer_tree_impl()->UnregisterPictureLayerImpl(this);
 }
 
+void PictureLayerImpl::SetLayerMaskType(Layer::LayerMaskType mask_type) {
+  if (mask_type_ == mask_type)
+    return;
+  DCHECK(mask_type_ != Layer::LayerMaskType::NOT_MASK &&

[enne (OOO), 2017/04/28 17:08:30]

Maybe leave a comment here saying that it's expected that a layer will never
change from being a mask to not being a mask, and that the only expected
conversion here is between multi -> single.

[sunxd, 2017/04/28 17:53:20]

Done.

+         mask_type != Layer::LayerMaskType::NOT_MASK);
+  mask_type_ = mask_type;
+}
+
 const char* PictureLayerImpl::LayerTypeAsString() const {
   return "cc::PictureLayerImpl";
 }
 
 std::unique_ptr<LayerImpl> PictureLayerImpl::CreateLayerImpl(
     LayerTreeImpl* tree_impl) {
   return PictureLayerImpl::Create(tree_impl, id(), mask_type());
 }
 
 void PictureLayerImpl::PushPropertiesTo(LayerImpl* base_layer) {
   PictureLayerImpl* layer_impl = static_cast<PictureLayerImpl*>(base_layer);
-  DCHECK_EQ(layer_impl->mask_type_, mask_type_);
 
   LayerImpl::PushPropertiesTo(base_layer);
 
+  layer_impl->SetLayerMaskType(mask_type());
   // Twin relationships should never change once established.
   DCHECK(!twin_layer_ || twin_layer_ == layer_impl);
   DCHECK(!twin_layer_ || layer_impl->twin_layer_ == this);
   // The twin relationship does not need to exist before the first
   // PushPropertiesTo from pending to active layer since before that the active
   // layer can not have a pile or tilings, it has only been created and inserted
   // into the tree at that point.
   twin_layer_ = layer_impl;
   layer_impl->twin_layer_ = this;
 
@@ skipping 1265 matching lines @@
   }
 
   invalidation_.Union(invalidation);
   tilings_->UpdateTilingsForImplSideInvalidation(invalidation);
   SetNeedsPushProperties();
   TRACE_EVENT_END1("cc", "PictureLayerImpl::InvalidateRegionForImages",
                    "Invalidation", invalidation.ToString());
 }
 
 }  // namespace cc