cc: Remove TiledLayer mask DCHECK for 0 tiles

cc/layers/tiled_layer_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/layers/tiled_layer_impl.h"
 
 #include "base/basictypes.h"
 #include "base/strings/stringprintf.h"
 #include "cc/base/math_util.h"
 #include "cc/debug/debug_colors.h"
@@ skipping 36 matching lines @@
 
 TiledLayerImpl::TiledLayerImpl(LayerTreeImpl* tree_impl, int id)
     : LayerImpl(tree_impl, id), skips_draw_(true) {}
 
 TiledLayerImpl::~TiledLayerImpl() {
 }
 
 ResourceProvider::ResourceId TiledLayerImpl::ContentsResourceId() const {
   // This function is only valid for single texture layers, e.g. masks.
   DCHECK(tiler_);
+  // It's possible the mask layer is created but has no size or otherwise
+  // can't draw.
+  if (tiler_->num_tiles_x() == 0 || tiler_->num_tiles_y() == 0)
+    return 0;
+
+  // Any other number of tiles other than 0 or 1 is incorrect for masks.
   DCHECK_EQ(tiler_->num_tiles_x(), 1);
   DCHECK_EQ(tiler_->num_tiles_y(), 1);
 
   DrawableTile* tile = TileAt(0, 0);
   ResourceProvider::ResourceId resource_id = tile ? tile->resource_id() : 0;
   return resource_id;
 }
 
 bool TiledLayerImpl::HasTileAt(int i, int j) const {
   return !!tiler_->TileAt(i, j);
@@ skipping 225 matching lines @@
 
 void TiledLayerImpl::ReleaseResources() {
   tiler_->reset();
 }
 
 const char* TiledLayerImpl::LayerTypeAsString() const {
   return "cc::TiledLayerImpl";
 }
 
 }  // namespace cc