Add cheapness predictor success histogram

cc/picture_pile_impl.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 "base/debug/trace_event.h"
 #include "cc/picture_pile_impl.h"
 #include "cc/region.h"
 #include "cc/rendering_stats.h"
 #include "third_party/skia/include/core/SkCanvas.h"
 #include "third_party/skia/include/core/SkSize.h"
@@ skipping 150 matching lines @@
       layer_rect.height(),
       SkPicture::kUsePathBoundsForClip_RecordingFlag);
 
   RenderingStats stats;
   Raster(canvas, layer_rect, 1.0, &stats);
   picture->endRecording();
 
   return picture;
 }
 
+bool PicturePileImpl::IsCheapInRect(
+    gfx::Rect content_rect, float contents_scale) const {
+  gfx::Rect layer_rect = gfx::ToEnclosingRect(
+      gfx::ScaleRect(content_rect, 1.f / contents_scale));
+
+  for (TilingData::Iterator tile_iter(&tiling_, layer_rect);
+       tile_iter; ++tile_iter) {
+    PictureListMap::const_iterator map_iter =
+        picture_list_map_.find(tile_iter.index());
+    if (map_iter == picture_list_map_.end())
+      continue;
+
+    const PictureList& pic_list = map_iter->second;
+    for (PictureList::const_iterator i = pic_list.begin();
+         i != pic_list.end(); ++i) {
+      if (!(*i)->LayerRect().Intersects(layer_rect) || !(*i)->HasRecording())
+        continue;
+      if (!(*i)->IsCheapInRect(layer_rect))

[Tom Hudson, 2013/02/06 12:24:57]

This layer_rect is the content_rect, inverse scaled by contents_scale.

The Picture in the iterator also has a layer_rect_, which often seems to be the
same in practice (and you check to make sure they intersect).

Shouldn't we be worried about the tile bounds somewhere?

+        return false;
+    }
+  }
+  return true;
+}
+
 }  // namespace cc