Make guard_cid and nullable_cid half words.

runtime/vm/assembler_ia32.h

Index: runtime/vm/assembler_ia32.h
diff --git a/runtime/vm/assembler_ia32.h b/runtime/vm/assembler_ia32.h
index 27d1c26f6204a34e8f87f3629b5e1afc4980c41c..1b386a3e95bf7c2eb82d4ef84469f95176991f40 100644
--- a/runtime/vm/assembler_ia32.h
+++ b/runtime/vm/assembler_ia32.h
@@ -356,6 +356,7 @@ class Assembler : public ValueObject {
   void movsxw(Register dst, const Address& src);
   void movw(Register dst, const Address& src);
   void movw(const Address& dst, Register src);
+  void movw(const Address& dst, const Immediate& imm);
 
   void leal(Register dst, const Address& src);
 
@@ -531,6 +532,8 @@ class Assembler : public ValueObject {
 
   void cmpl(const Address& address, Register reg);
   void cmpl(const Address& address, const Immediate& imm);
+  void cmpw(Register reg, const Address& address);
+  void cmpw(const Address& address, const Immediate& imm);
   void cmpb(const Address& address, const Immediate& imm);
 
   void testl(Register reg1, Register reg2);