Improvements to uses of base::SmallMap

cc/tiles/picture_layer_tiling.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/tiles/picture_layer_tiling.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <cmath>
@@ skipping 239 matching lines @@
   DCHECK(tree_ != ACTIVE_TREE || !client_->GetPendingOrActiveTwinTiling(this));
   RemoveTilesInRegion(layer_invalidation, true /* recreate tiles */);
 }
 
 void PictureLayerTiling::RemoveTilesInRegion(const Region& layer_invalidation,
                                              bool recreate_tiles) {
   // We only invalidate the active tiling when it's orphaned: it has no pending
   // twin, so it's slated for removal in the future.
   if (live_tiles_rect_.IsEmpty())
     return;
-  // Pick 16 for the size of the SmallMap before it promotes to a unordered_map.
-  // 4x4 tiles should cover most small invalidations, and walking a vector of
-  // 16 is fast enough. If an invalidation is huge we will fall back to a
-  // unordered_map instead of a vector in the SmallMap.
-  base::SmallMap<std::unordered_map<TileMapKey, gfx::Rect, TileMapKeyHash>, 16>
+  // Pick 16 for the size of the small_map before it promotes to a
+  // unordered_map. 4x4 tiles should cover most small invalidations, and
+  // walking a vector of 16 is fast enough. If an invalidation is huge we will
+  // fall back to a unordered_map instead of a vector in the small_map.
+  base::small_map<std::unordered_map<TileMapKey, gfx::Rect, TileMapKeyHash>, 16>

[danakj, 2017/04/18 21:35:50]

This should be a flat_map too

       remove_tiles;
   gfx::Rect expanded_live_tiles_rect =
       tiling_data_.ExpandRectToTileBounds(live_tiles_rect_);
   for (Region::Iterator iter(layer_invalidation); iter.has_rect();
        iter.next()) {
     gfx::Rect layer_rect = iter.rect();
     // The pixels which are invalid in content space.
     gfx::Rect invalid_content_rect =
         EnclosingContentsRectFromLayerRect(layer_rect);
     gfx::Rect coverage_content_rect = invalid_content_rect;
@@ skipping 674 matching lines @@
   return ToEnclosingRect(raster_transform_.MapRect(gfx::RectF(layer_rect)));
 }
 
 gfx::Rect PictureLayerTiling::EnclosingLayerRectFromContentsRect(
     const gfx::Rect& contents_rect) const {
   return ToEnclosingRect(
       raster_transform_.InverseMapRect(gfx::RectF(contents_rect)));
 }
 
 }  // namespace cc