Use BBH reserve hook to preallocate space for tiles.

src/core/SkTileGrid.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkTileGrid_DEFINED
 #define SkTileGrid_DEFINED
 
@@ skipping 21 matching lines @@
 
     /**
      * Populate 'results' with opIndexes corresponding to bounding boxes that intersect 'query'.
      * This will be fastest if the query is an exact match to a single grid tile.
      */
     virtual void search(const SkRect& query, SkTDArray<unsigned>* results) const SK_OVERRIDE;
 
     // For testing.
     int tileCount(int x, int y) { return fTiles[y * fXTiles + x].count(); }
 
+    virtual void reserve(unsigned opCount) SK_OVERRIDE;
+    virtual void flushDeferredInserts() SK_OVERRIDE;
+
 private:
     void commonAdjust(SkRect*) const;
     void userToGrid(const SkRect&, SkIRect* grid) const;
 
     const int fXTiles, fYTiles;
     const SkScalar fInvWidth, fInvHeight;
     const SkScalar fMarginWidth, fMarginHeight;
     const SkPoint fOffset;
     const SkRect  fGridBounds;
 
     // (fXTiles * fYTiles) SkTDArrays, each listing ops overlapping that tile in order.
     SkTDArray<unsigned>* fTiles;
 
     typedef SkBBoxHierarchy INHERITED;
 };
 
 #endif