Move GetRootListIndex into Heap.

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index 4a5052310efaddd209c8c9bc0ce65cbf9defda74..f106bbfe0abfe1842950b071106737c8e338edf6 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -1166,6 +1166,10 @@ class Heap {
     kSmiRootsStart = kStringTableRootIndex + 1
   };
 
+  // Get the root list index for {object} if such a root list index exists.
+  bool GetRootListIndex(Handle<HeapObject> object,
+                        Heap::RootListIndex* index_return);
+
   Object* root(RootListIndex index) { return roots_[index]; }
 
   STATIC_ASSERT(kUndefinedValueRootIndex ==