Add 64-bit stubs to call into the runtime and to call native functions.

runtime/vm/runtime_entry.h

Index: runtime/vm/runtime_entry.h
===================================================================
--- runtime/vm/runtime_entry.h	(revision 2106)
+++ runtime/vm/runtime_entry.h	(working copy)
@@ -33,6 +33,11 @@
   int argument_count() const { return argument_count_; }
   uword GetEntryPoint() const { return reinterpret_cast<uword>(function()); }
 
+  // Add function to a class and that class to the class dictionary so that
+  // frame walking can be used (for testing purposes only).
+  static const Function& RegisterFakeFunction(const char* name,
+                                              const Code& code);
+
   // Generate code to call the runtime entry.
   void CallFromDart(Assembler* assembler) const;
   void CallFromStub(Assembler* assembler) const;