Support correct factory syntax in the VM as decribed in the spec.

runtime/vm/object.h

Index: runtime/vm/object.h
===================================================================
--- runtime/vm/object.h	(revision 1593)
+++ runtime/vm/object.h	(working copy)
@@ -451,13 +451,21 @@
   // Asserts that the class of the super type has been resolved.
   RawClass* SuperClass() const;
 
-  // The factory type of this interface, null if not specified.
-  RawType* factory_type() const { return raw_ptr()->factory_type_; }
-  void set_factory_type(const Type& value) const;
+  // Return true if this interface has a factory class.
+  bool HasFactoryClass() const;
 
-  // Asserts that the class of the factory type has been resolved.
+  // Return true if the factory class of this interface is resolved.
+  bool HasResolvedFactoryClass() const;
+
+  // Return the resolved factory class of this interface.
   RawClass* FactoryClass() const;
 
+  // Return the unresolved factory class of this interface.
+  RawUnresolvedClass* UnresolvedFactoryClass() const;
+
+  // Set the resolved or unresolved factory class of this interface.
+  void set_factory_class(const Object& value) const;
+
   // Interfaces is an array of Types.
   RawArray* interfaces() const { return raw_ptr()->interfaces_; }
   void set_interfaces(const Array& value) const;
@@ -644,6 +652,11 @@
   RawString* ident() const { return raw_ptr()->ident_; }
   intptr_t token_index() const { return raw_ptr()->token_index_; }
 
+  RawClass* factory_signature_class() const {
+    return raw_ptr()->factory_signature_class_;
+  }
+  void set_factory_signature_class(const Class& value) const;
+
   RawString* Name() const;
 
   static intptr_t InstanceSize() {