Enable optimization of top-level code.

src/x64/lithium-x64.h

Index: src/x64/lithium-x64.h
===================================================================
--- src/x64/lithium-x64.h	(revision 10686)
+++ src/x64/lithium-x64.h	(working copy)
@@ -87,6 +87,7 @@
   V(ConstantI)                                  \
   V(ConstantT)                                  \
   V(Context)                                    \
+  V(DeclareGlobals)                             \
   V(DeleteProperty)                             \
   V(Deoptimize)                                 \
   V(DivI)                                       \
@@ -1345,6 +1346,13 @@
 };
 
 
+class LDeclareGlobals: public LTemplateInstruction<0, 0, 0> {
+ public:
+  DECLARE_CONCRETE_INSTRUCTION(DeclareGlobals, "declare-globals")
+  DECLARE_HYDROGEN_ACCESSOR(DeclareGlobals)
+};
+
+
 class LGlobalObject: public LTemplateInstruction<1, 0, 0> {
  public:
   DECLARE_CONCRETE_INSTRUCTION(GlobalObject, "global-object")