Move Maps' back pointers from "transitions" to "constructor" field

src/ia32/lithium-codegen-ia32.cc

Index: src/ia32/lithium-codegen-ia32.cc
diff --git a/src/ia32/lithium-codegen-ia32.cc b/src/ia32/lithium-codegen-ia32.cc
index 1b21781dc7ce596aecce0b747f9a1c4ed9f76700..bffd7cf6f297665fc8689ac6433bef9312bdd591 100644
--- a/src/ia32/lithium-codegen-ia32.cc
+++ b/src/ia32/lithium-codegen-ia32.cc
@@ -2581,9 +2581,9 @@ void LCodeGen::EmitClassOfTest(Label* is_true,
 
   // Now we are in the FIRST-LAST_NONCALLABLE_SPEC_OBJECT_TYPE range.
   // Check if the constructor in the map is a function.
-  __ mov(temp, FieldOperand(temp, Map::kConstructorOffset));
+  __ GetMapConstructor(temp, temp, temp2);
   // Objects with a non-function constructor have class 'Object'.
-  __ CmpObjectType(temp, JS_FUNCTION_TYPE, temp2);
+  __ CmpInstanceType(temp2, JS_FUNCTION_TYPE);
   if (String::Equals(class_name, isolate()->factory()->Object_string())) {
     __ j(not_equal, is_true);
   } else {