Introduce safe interface to "copy and grow" FixedArray.

src/factory.h

Index: src/factory.h
diff --git a/src/factory.h b/src/factory.h
index 9a595c411566288711fccba9a1a8e68908609b18..c52d6d31d94c2543881198c93e5de18ccfc1dca7 100644
--- a/src/factory.h
+++ b/src/factory.h
@@ -322,6 +322,9 @@ class Factory final {
   Handle<FixedArray> CopyFixedArrayWithMap(Handle<FixedArray> array,
                                            Handle<Map> map);
 
+  Handle<FixedArray> CopyFixedArrayAndGrow(Handle<FixedArray> array,
+                                           int grow_by);
+
   Handle<FixedArray> CopyFixedArray(Handle<FixedArray> array);
 
   // This method expects a COW array in new space, and creates a copy