Support verified heap pointer writes on ia32.

runtime/vm/assembler_ia32.h

Index: runtime/vm/assembler_ia32.h
===================================================================
--- runtime/vm/assembler_ia32.h	(revision 41609)
+++ runtime/vm/assembler_ia32.h	(working copy)
@@ -679,6 +679,7 @@
 
   // Stores a Smi value into a heap object field that always contains a Smi.
   void StoreIntoSmiField(const Address& dest, Register value);
+  void ZeroSmiField(const Address& dest);
   // Increments a Smi field. Leaves flags in same state as an 'addl'.
   void IncrementSmiField(const Address& dest, int32_t increment);
 
@@ -928,6 +929,10 @@
                                   Register value,
                                   Label* no_update);
 
+  // Private helpers for write barrier verification.
+  void VerifiedWrite(const Address& dest, Register value);
+  void UnverifiedStoreOldObject(const Address& dest, const Object& value);
+
   int32_t jit_cookie();
 
   AssemblerBuffer buffer_;