Gentle start with removing explicit interfaces

runtime/vm/object.h

Index: runtime/vm/object.h
===================================================================
--- runtime/vm/object.h	(revision 11241)
+++ runtime/vm/object.h	(working copy)
@@ -874,14 +874,14 @@
   // Check if this type represents the 'double' interface.
   bool IsDoubleInterface() const;
 
-  // Check if this type represents the 'num' interface.
-  bool IsNumberInterface() const;
+  // Check if this type represents the 'num' type.
+  bool IsNumberType() const;
 
   // Check if this type represents the 'String' interface.
   bool IsStringInterface() const;
 
-  // Check if this type represents the 'Function' interface.
-  bool IsFunctionInterface() const;
+  // Check if this type represents the 'Function' type.
+  bool IsFunctionType() const;
 
   // Check if this type represents the 'List' interface.
   bool IsListInterface() const;
@@ -993,13 +993,13 @@
   static RawType* DoubleInterface();
 
   // The 'num' interface type.
-  static RawType* NumberInterface();
+  static RawType* Number();
 
   // The 'String' interface type.
   static RawType* StringInterface();
 
   // The 'Function' interface type.
-  static RawType* FunctionInterface();
+  static RawType* Function();
 
   // The 'List' interface type.
   static RawType* ListInterface();
@@ -3144,6 +3144,7 @@
     return false;
   }
   OBJECT_IMPLEMENTATION(Number, Instance);
+  friend class Class;
 };
 
 
@@ -5229,6 +5230,15 @@
 };
 
 
+// DartFunction represents the abstract Dart class 'Function'.
+class DartFunction : public Instance {
+ private:
+  HEAP_OBJECT_IMPLEMENTATION(DartFunction, Instance);
+  friend class Class;
+  friend class Instance;
+};
+
+
 class Closure : public Instance {
  public:
   RawFunction* function() const { return raw_ptr()->function_; }