Use Object::null_object() instead of Object::ZoneHandle() when a null object

runtime/vm/flow_graph_compiler_ia32.cc

Index: runtime/vm/flow_graph_compiler_ia32.cc
===================================================================
--- runtime/vm/flow_graph_compiler_ia32.cc	(revision 37955)
+++ runtime/vm/flow_graph_compiler_ia32.cc	(working copy)
@@ -603,7 +603,7 @@
     // Generate runtime call.
     __ movl(EDX, Address(ESP, 0));  // Get instantiator type arguments.
     __ movl(ECX, Address(ESP, kWordSize));  // Get instantiator.
-    __ PushObject(Object::ZoneHandle());  // Make room for the result.
+    __ PushObject(Object::null_object());  // Make room for the result.
     __ pushl(EAX);  // Push the instance.
     __ PushObject(type);  // Push the type.
     __ pushl(ECX);  // Instantiator.
@@ -675,7 +675,7 @@
 
   // Generate throw new TypeError() if the type is malformed or malbounded.
   if (dst_type.IsMalformedOrMalbounded()) {
-    __ PushObject(Object::ZoneHandle());  // Make room for the result.
+    __ PushObject(Object::null_object());  // Make room for the result.
     __ pushl(EAX);  // Push the source object.
     __ PushObject(dst_name);  // Push the name of the destination.
     __ PushObject(dst_type);  // Push the type of the destination.
@@ -701,7 +701,7 @@
   __ Bind(&runtime_call);
   __ movl(EDX, Address(ESP, 0));  // Get instantiator type arguments.
   __ movl(ECX, Address(ESP, kWordSize));  // Get instantiator.
-  __ PushObject(Object::ZoneHandle());  // Make room for the result.
+  __ PushObject(Object::null_object());  // Make room for the result.
   __ pushl(EAX);  // Push the source object.
   __ PushObject(dst_type);  // Push the type of the destination.
   __ pushl(ECX);  // Instantiator.