Update SkPicture cull rects with RTree information

src/core/SkRTree.cpp

Index: src/core/SkRTree.cpp
diff --git a/src/core/SkRTree.cpp b/src/core/SkRTree.cpp
index ba5843e537eaba6b3f90862132e5c0dc29d7f77e..2fded6f72bd396be27b3e49d7614639bab99937e 100644
--- a/src/core/SkRTree.cpp
+++ b/src/core/SkRTree.cpp
@@ -9,6 +9,14 @@
 
 SkRTree::SkRTree(SkScalar aspectRatio) : fCount(0), fAspectRatio(aspectRatio) {}
 
+SkRect SkRTree::getRootBound() const {
+    if (fCount) {
+        return fRoot.fBounds;
+    } else {
+        return SkRect::MakeEmpty();
+    }
+}
+
 void SkRTree::insert(const SkRect boundsArray[], int N) {
     SkASSERT(0 == fCount);