cc: Generate tilings at other scales for impl-side painting

cc/picture_layer_tiling_set.h

Index: cc/picture_layer_tiling_set.h
diff --git a/cc/picture_layer_tiling_set.h b/cc/picture_layer_tiling_set.h
index 383884e1de1afca8038c2b1ad4cc3bc6af024c78..72b583ec58f0ef3cc4ac150310e0550a08d88f2d 100644
--- a/cc/picture_layer_tiling_set.h
+++ b/cc/picture_layer_tiling_set.h
@@ -26,13 +26,20 @@ class CC_EXPORT PictureLayerTilingSet {
   void SetLayerBounds(gfx::Size layer_bounds);
   gfx::Size LayerBounds() const;
 
-  const PictureLayerTiling* AddTiling(
+  PictureLayerTiling* AddTiling(
       float contents_scale,
       gfx::Size tile_size);
   size_t num_tilings() const { return tilings_.size(); }
   PictureLayerTiling* tiling_at(size_t idx) { return tilings_[idx]; }
 
-  void Reset();
+  // Remove all tilings.
+  void RemoveAllTilings();
+
+  // Remove one tiling.
+  void Remove(PictureLayerTiling* tiling);
+
+  // Remove all tiles; keep all tilings.
+  void RemoveAllTiles();
 
   void UpdateTilePriorities(
       WhichTree tree,
@@ -53,7 +60,8 @@ class CC_EXPORT PictureLayerTilingSet {
     Iterator(
       const PictureLayerTilingSet* set,
       float contents_scale,
-      gfx::Rect rect);
+      gfx::Rect content_rect,
+      float ideal_contents_scale);
     ~Iterator();
 
     // Visible rect (no borders), always in the space of rect,
@@ -70,11 +78,17 @@ class CC_EXPORT PictureLayerTilingSet {
     Iterator& operator++();
     operator bool() const;
 
+    PictureLayerTiling* CurrentTiling();
+
    private:
+    int NextTiling() const;
+
     const PictureLayerTilingSet* set_;
     float contents_scale_;
+    float ideal_contents_scale_;
     PictureLayerTiling::Iterator tiling_iter_;
     int current_tiling_;
+    int ideal_tiling_;
 
     Region current_region_;
     Region missing_region_;