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

src/arm/lithium-codegen-arm.cc

Index: src/arm/lithium-codegen-arm.cc
diff --git a/src/arm/lithium-codegen-arm.cc b/src/arm/lithium-codegen-arm.cc
index 36502abe2b74b2f2f6abdd8c0aacd539d460abd7..ef1abbb01ce4fa7ddb55755763a309e3a409ed68 100644
--- a/src/arm/lithium-codegen-arm.cc
+++ b/src/arm/lithium-codegen-arm.cc
@@ -2730,10 +2730,11 @@ 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.
-  __ ldr(temp, FieldMemOperand(temp, Map::kConstructorOffset));
+  Register instance_type = ip;
+  __ GetMapConstructor(temp, temp, temp2, instance_type);
 
   // Objects with a non-function constructor have class 'Object'.
-  __ CompareObjectType(temp, temp2, temp2, JS_FUNCTION_TYPE);
+  __ cmp(instance_type, Operand(JS_FUNCTION_TYPE));
   if (class_name->IsOneByteEqualTo(STATIC_CHAR_VECTOR("Object"))) {
     __ b(ne, is_true);
   } else {