cc: Do GatherPixelRefs from skia at record time

cc/resources/picture_pile_impl.cc

Index: cc/resources/picture_pile_impl.cc
diff --git a/cc/resources/picture_pile_impl.cc b/cc/resources/picture_pile_impl.cc
index 397d64c0d97490d062f918a5bdddcce8e4c49158..d80737890864d6e1a70c0ae4392754aa2118497e 100644
--- a/cc/resources/picture_pile_impl.cc
+++ b/cc/resources/picture_pile_impl.cc
@@ -198,31 +198,6 @@ int64 PicturePileImpl::Raster(
   return total_pixels_rasterized;
 }
 
-void PicturePileImpl::GatherPixelRefs(
-    gfx::Rect content_rect,
-    float contents_scale,
-    std::list<skia::LazyPixelRef*>& pixel_refs) {
-  std::list<skia::LazyPixelRef*> result;
-
-  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::iterator map_iter =
-        picture_list_map_.find(tile_iter.index());
-    if (map_iter == picture_list_map_.end())
-      continue;
-
-    PictureList& pic_list = map_iter->second;
-    for (PictureList::const_iterator i = pic_list.begin();
-         i != pic_list.end(); ++i) {
-      (*i)->GatherPixelRefs(layer_rect, result);
-      pixel_refs.splice(pixel_refs.end(), result);
-    }
-  }
-}
-
 skia::RefPtr<SkPicture> PicturePileImpl::GetFlattenedPicture() {
   TRACE_EVENT0("cc", "PicturePileImpl::GetFlattenedPicture");
 
@@ -276,4 +251,59 @@ PicturePileImpl::Analysis::Analysis()
 PicturePileImpl::Analysis::~Analysis() {
 }
 
+PicturePileImpl::LazyPixelRefsIterator::LazyPixelRefsIterator(
+    gfx::Rect content_rect,
+    float contents_scale,
+    const PicturePileImpl* picture_pile)
+    : picture_pile_(picture_pile),
+      layer_rect_(gfx::ToEnclosingRect(
+          gfx::ScaleRect(content_rect, 1.f / contents_scale))),
+      tile_iterator_(&picture_pile_->tiling_, layer_rect_),
+      current_pixel_ref_(NULL) {
+  ++(*this);
+}
+
+PicturePileImpl::LazyPixelRefsIterator::~LazyPixelRefsIterator() {
+}
+
+PicturePileImpl::LazyPixelRefsIterator&
+    PicturePileImpl::LazyPixelRefsIterator::operator++() {
+  while (true) {
+    // If there are still pixel refs on the current picture,
+    // advance the picture refs iterator.
+    if (picture_refs_iterator_) {
+      current_pixel_ref_ = *picture_refs_iterator_;
+      ++picture_refs_iterator_;
+      break;
+    }
+
+    // If there are pictures left in the current tile's list, process them.
+    if (!picture_list_.empty()) {
+      scoped_refptr<Picture> picture = picture_list_.front();
+      picture_list_.pop_front();
+      picture_refs_iterator_ = Picture::LazyPixelRefsIterator(
+          layer_rect_,
+          picture.get());
+      continue;
+    }
+
+    // If we're out of tiles, we're done.
+    if (!tile_iterator_) {
+      current_pixel_ref_ = NULL;
+      break;
+    }
+
+    // Grab a new picture list from the current tile,
+    // and advance the tile iterator.
+    PictureListMap::const_iterator map_iterator =
+        picture_pile_->picture_list_map_.find(tile_iterator_.index());
+    ++tile_iterator_;
+    if (map_iterator == picture_pile_->picture_list_map_.end())
+      continue;
+
+    picture_list_ = map_iterator->second;
+  }
+  return *this;
+}
+
 }  // namespace cc