Makes tile-creation lazy

cc/resources/picture_layer_tiling.h

Index: cc/resources/picture_layer_tiling.h
diff --git a/cc/resources/picture_layer_tiling.h b/cc/resources/picture_layer_tiling.h
index 5a83e40696f99e78870386ed1a18a85887b42e45..426a76fa7cf20872ae33a8b7879ed88a9b066197 100644
--- a/cc/resources/picture_layer_tiling.h
+++ b/cc/resources/picture_layer_tiling.h
@@ -32,8 +32,10 @@ class PictureLayerTilingClient {
     gfx::Rect content_rect) = 0;
   virtual void UpdatePile(Tile* tile) = 0;
   virtual gfx::Size CalculateTileSize(
-    gfx::Size current_tile_size,
     gfx::Size content_bounds) = 0;
+  virtual const Region* GetInvalidation() = 0;
+  virtual const PictureLayerTiling* GetTwinTiling(
+      const PictureLayerTiling* tiling) = 0;
 
  protected:
   virtual ~PictureLayerTilingClient() {}
@@ -44,17 +46,17 @@ class CC_EXPORT PictureLayerTiling {
   ~PictureLayerTiling();
 
   // Create a tiling with no tiles.  CreateTiles must be called to add some.
-  static scoped_ptr<PictureLayerTiling> Create(float contents_scale);
-  scoped_ptr<PictureLayerTiling> Clone() const;
-
+  static scoped_ptr<PictureLayerTiling> Create(
+      float contents_scale,
+      gfx::Size layer_bounds,
+      PictureLayerTilingClient* client);
+  scoped_ptr<PictureLayerTiling> Clone(gfx::Size layer_bounds,
+                                       PictureLayerTilingClient* client) const;
   gfx::Size layer_bounds() const { return layer_bounds_; }
-  void SetLayerBounds(gfx::Size layer_bounds);
-  void Invalidate(const Region& layer_invalidation);
   void InvalidateTilesWithText();
 
   // Add any tiles that intersect with |layer_rect|.  If any tiles already
   // exist, then this leaves them as-is.
-  void CreateTilesFromLayerRect(gfx::Rect layer_rect);
 
   void SetClient(PictureLayerTilingClient* client);
   void set_resolution(TileResolution resolution) { resolution_ = resolution; }
@@ -64,6 +66,10 @@ class CC_EXPORT PictureLayerTiling {
   gfx::SizeF ContentSizeF() const;
   float contents_scale() const { return contents_scale_; }
 
+  void CreateAllTilesForTesting() {
+    SetLiveTilesRect(gfx::Rect(tiling_data_.total_size()));
+  }
+
   std::vector<Tile*> AllTilesForTesting() const {
     std::vector<Tile*> all_tiles;
     for (TileMap::const_iterator it = tiles_.begin();
@@ -72,11 +78,6 @@ class CC_EXPORT PictureLayerTiling {
     return all_tiles;
   }
 
-  static gfx::Rect ExpandRectEquallyToAreaBoundedBy(
-      gfx::Rect starting_rect,
-      int64 target_area,
-      gfx::Rect bounding_rect);
-
   // Iterate over all tiles to fill content_rect.  Even if tiles are invalid
   // (i.e. no valid resource) this tiling should still iterate over them.
   // The union of all geometry_rect calls for each element iterated over should
@@ -125,7 +126,7 @@ class CC_EXPORT PictureLayerTiling {
 
   Region OpaqueRegionInContentRect(const gfx::Rect&) const;
 
-  void Reset() { return tiles_.clear(); }
+  void Reset();
 
   void UpdateTilePriorities(
       WhichTree tree,
@@ -149,23 +150,34 @@ class CC_EXPORT PictureLayerTiling {
 
   scoped_ptr<base::Value> AsValue() const;
 
+  static gfx::Rect ExpandRectEquallyToAreaBoundedBy(
+      gfx::Rect starting_rect,
+      int64 target_area,
+      gfx::Rect bounding_rect);
+
  protected:
   typedef std::pair<int, int> TileMapKey;
   typedef base::hash_map<TileMapKey, scoped_refptr<Tile> > TileMap;
 
-  explicit PictureLayerTiling(float contents_scale);
-  Tile* TileAt(int, int) const;
-  void CreateTilesFromContentRect(gfx::Rect layer_rect);
+  PictureLayerTiling(float contents_scale,
+                     gfx::Size layer_bounds,
+                     PictureLayerTilingClient* client);
+  void SetLiveTilesRect(gfx::Rect live_tiles_rect);
   void CreateTile(int i, int j);
+  Tile* TileAt(int, int) const;
 
-  PictureLayerTilingClient* client_;
+  // Given properties.
   float contents_scale_;
   gfx::Size layer_bounds_;
-  gfx::Rect last_prioritized_rect_;
-  // It is not legal to have a NULL tile in the tiles_ map.
-  TileMap tiles_;
-  TilingData tiling_data_;
   TileResolution resolution_;
+  PictureLayerTilingClient* client_;
+
+  // Internal data.
+  TilingData tiling_data_;
+  TileMap tiles_;  // It is not legal to have a NULL tile in the tiles_ map.
+  gfx::Rect live_tiles_rect_;
+
+  // State saved for computing velocities based upon finite differences.
   int last_source_frame_number_;
   double last_impl_frame_time_;