Add a cache of LayerImpl's viewport layer type

cc/trees/layer_tree_host_impl_unittest.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_host_impl.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <cmath>
@@ skipping 288 matching lines @@
       if (scroll_info.scrolls[i].layer_id != id)
         continue;
       times_encountered++;
     }
 
     ASSERT_EQ(0, times_encountered);
   }
 
   LayerImpl* CreateScrollAndContentsLayers(LayerTreeImpl* layer_tree_impl,
                                            const gfx::Size& content_size) {
+    // Clear any existing viewport layers that were setup so this function can
+    // be called multiple times.
+    layer_tree_impl->ClearViewportLayers();
+
     // Create both an inner viewport scroll layer and an outer viewport scroll
     // layer. The MaxScrollOffset of the outer viewport scroll layer will be
     // 0x0, so the scrolls will be applied directly to the inner viewport.
     const int kOuterViewportClipLayerId = 116;
     const int kOuterViewportScrollLayerId = 117;
     const int kContentLayerId = 118;
     const int kInnerViewportScrollLayerId = 2;
     const int kInnerViewportClipLayerId = 4;
     const int kPageScaleLayerId = 5;
 
@@ skipping 12048 matching lines @@
     else
       EXPECT_FALSE(tile->HasRasterTask());
   }
   Region expected_invalidation(
       raster_source->GetRectForImage(checkerable_image->uniqueID()));
   EXPECT_EQ(expected_invalidation, *(root->GetPendingInvalidation()));
 }
 
 }  // namespace
 }  // namespace cc