Heap profiler: account primitive string objects as being constructed using 'String'.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index bd8ca513ba34bfebec5155993d57890c605a8360..ca9c6b15781348f0b791b997801ccc74b5ce7b2e 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -1392,6 +1392,10 @@ class JSObject: public HeapObject {
   // Returns the class name ([[Class]] property in the specification).
   String* class_name();
 
+  // Returns the constructor name (the name (possibly, inferred name) of the
+  // function that was used to instantiate the object).
+  String* constructor_name();
+
   // Retrieve interceptors.
   InterceptorInfo* GetNamedInterceptor();
   InterceptorInfo* GetIndexedInterceptor();