Gentle start with removing explicit interfaces

runtime/vm/object.h

Index: runtime/vm/object.h
===================================================================
--- runtime/vm/object.h	(revision 11079)
+++ runtime/vm/object.h	(working copy)
@@ -875,13 +875,13 @@
   bool IsDoubleInterface() const;
 
   // Check if this type represents the 'num' interface.
-  bool IsNumberInterface() const;
+  bool IsNumber() 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 IsFunction() 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();