X87: [stubs] Optimize LoadGlobalViaContextStub and StoreGlobalViaContextStub.

src/x87/macro-assembler-x87.h

Index: src/x87/macro-assembler-x87.h
diff --git a/src/x87/macro-assembler-x87.h b/src/x87/macro-assembler-x87.h
index 71d538746793210a138a885bdc4c18b7d4331844..02e567dde05691140ba8127c82ca5c7a7cf3bdd5 100644
--- a/src/x87/macro-assembler-x87.h
+++ b/src/x87/macro-assembler-x87.h
@@ -1022,6 +1022,11 @@ inline Operand ContextOperand(Register context, int index) {
 }
 
 
+inline Operand ContextOperand(Register context, Register index) {
+  return Operand(context, index, times_pointer_size, Context::SlotOffset(0));
+}
+
+
 inline Operand GlobalObjectOperand() {
   return ContextOperand(esi, Context::GLOBAL_OBJECT_INDEX);
 }