Added support for assignments to global variables in the toplevel code...

src/x64/codegen-x64.h

Index: src/x64/codegen-x64.h
===================================================================
--- src/x64/codegen-x64.h	(revision 3091)
+++ src/x64/codegen-x64.h	(working copy)
@@ -398,7 +398,7 @@
   void LoadReference(Reference* ref);
   void UnloadReference(Reference* ref);
 
-  Operand ContextOperand(Register context, int index) const {
+  static Operand ContextOperand(Register context, int index) {
     return Operand(context, Context::SlotOffset(index));
   }
 
@@ -409,7 +409,7 @@
                                             JumpTarget* slow);
 
   // Expressions
-  Operand GlobalObject() const {
+  static Operand GlobalObject() {
     return ContextOperand(rsi, Context::GLOBAL_INDEX);
   }
 
@@ -616,6 +616,7 @@
   friend class JumpTarget;
   friend class Reference;
   friend class Result;
+  friend class FastCodeGenerator;
 
   friend class CodeGeneratorPatcher;  // Used in test-log-stack-tracer.cc