cc: Compute picture pile size at construction time.

cc/resources/picture_pile_impl.h

Index: cc/resources/picture_pile_impl.h
diff --git a/cc/resources/picture_pile_impl.h b/cc/resources/picture_pile_impl.h
index 4b7af420840dbd66ebd6b2b178e220e6b7ef8db8..1d085c1c3415a2f251e774d7aafd4ad5e4518f64 100644
--- a/cc/resources/picture_pile_impl.h
+++ b/cc/resources/picture_pile_impl.h
@@ -124,6 +124,8 @@ class CC_EXPORT PicturePileImpl : public RasterSource {
   // threads with multi-threaded Ganesh.  Make this const or remove it.
   bool should_attempt_to_use_distance_field_text_;
 
+  size_t picture_memory_usage_;
+
  private:
   typedef std::map<const Picture*, Region> PictureRegionMap;