[es6] Introduce a dedicated JSIteratorResult type.

src/x64/macro-assembler-x64.h

Index: src/x64/macro-assembler-x64.h
diff --git a/src/x64/macro-assembler-x64.h b/src/x64/macro-assembler-x64.h
index 769b91b4862c03d46200ab7acbefd5cc88c6c357..63feb828407b11f8c39bfeda27bceeb898d5824a 100644
--- a/src/x64/macro-assembler-x64.h
+++ b/src/x64/macro-assembler-x64.h
@@ -133,6 +133,10 @@ class MacroAssembler: public Assembler {
 
   // Operations on roots in the root-array.
   void LoadRoot(Register destination, Heap::RootListIndex index);
+  void LoadRoot(const Operand& destination, Heap::RootListIndex index) {
+    LoadRoot(kScratchRegister, index);
+    movp(destination, kScratchRegister);
+  }
   void StoreRoot(Register source, Heap::RootListIndex index);
   // Load a root value where the index (or part of it) is variable.
   // The variable_offset register is added to the fixed_offset value