Move visual rect unioning between paired items to cc::DisplayItemList.

cc/playback/display_item_list.cc

Index: cc/playback/display_item_list.cc
diff --git a/cc/playback/display_item_list.cc b/cc/playback/display_item_list.cc
index 24736f4e184ae3c4e05de7d77ba5bce6a7913ea6..1f2c6bed0c076ab723e302282da556ff4d98b1df 100644
--- a/cc/playback/display_item_list.cc
+++ b/cc/playback/display_item_list.cc
@@ -164,6 +164,12 @@ void DisplayItemList::Raster(SkCanvas* canvas,
   }
 }
 
+void DisplayItemList::GrowCurrentBeginItemVisualRect(
+    const gfx::Rect& visual_rect) {
+  if (!inputs_.begin_item_indices.empty())
+    inputs_.visual_rects[inputs_.begin_item_indices.back()].Union(visual_rect);
+}
+
 void DisplayItemList::ProcessAppendedItem(const DisplayItem* item) {
   if (inputs_.settings.use_cached_picture) {
     DCHECK(recorder_);