cc: Fix crash in MVRAR with missing recordings

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 <algorithm>
 
 #include "base/time.h"
 #include "cc/base/math_util.h"
@@ skipping 664 matching lines @@
     if (tiling->resolution() == HIGH_RESOLUTION) {
       DCHECK(!high_res) << "There can only be one high res tiling";
       high_res = tiling;
       continue;
     }
     for (PictureLayerTiling::CoverageIterator iter(tiling,
                                                    contents_scale_x(),
                                                    rect);
          iter;
          ++iter) {
-      if (!iter->tile_version().IsReadyToDraw())
+      if (!*iter || !iter->tile_version().IsReadyToDraw())
         continue;
       missing_region.Subtract(iter.geometry_rect());
       iter->mark_required_for_activation();
 
       DCHECK_EQ(iter->priority(PENDING_TREE).distance_to_visible_in_pixels, 0);
       DCHECK_EQ(iter->priority(PENDING_TREE).time_to_visible_in_seconds, 0);
     }
   }
 
   DCHECK(high_res) << "There must be one high res tiling";
@@ skipping 318 matching lines @@
   state->Set("tilings", tilings_->AsValue().release());
   state->Set("pictures", pile_->AsValue().release());
   state->Set("invalidation", invalidation_.AsValue().release());
 }
 
 size_t PictureLayerImpl::GPUMemoryUsageInBytes() const {
   return tilings_->GPUMemoryUsageInBytes();
 }
 
 }  // namespace cc