Cleanup of contexts in the full code generator.

src/x64/macro-assembler-x64.h

Index: src/x64/macro-assembler-x64.h
===================================================================
--- src/x64/macro-assembler-x64.h	(revision 5450)
+++ src/x64/macro-assembler-x64.h	(working copy)
@@ -520,6 +520,9 @@
   void Set(Register dst, int64_t x);
   void Set(const Operand& dst, int64_t x);
 
+  // Move if the registers are not identical.
+  void Move(Register target, Register source);
+
   // Handle support
   void Move(Register dst, Handle<Object> source);
   void Move(const Operand& dst, Handle<Object> source);