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

src/arm/macro-assembler-arm.cc

Index: src/arm/macro-assembler-arm.cc
diff --git a/src/arm/macro-assembler-arm.cc b/src/arm/macro-assembler-arm.cc
index c8fb60dafa93bb614d9afbe3701e00dbcab11b10..2b723b38baefda9126a2730eea1901221f59c38e 100644
--- a/src/arm/macro-assembler-arm.cc
+++ b/src/arm/macro-assembler-arm.cc
@@ -2292,6 +2292,20 @@ void MacroAssembler::LoadWeakValue(Register value, Handle<WeakCell> cell,
 }
 
 
+void MacroAssembler::GetMapConstructor(Register result, Register map,
+                                       Register temp, Register temp2) {
+  Label done, loop;
+  ldr(result, FieldMemOperand(map, Map::kConstructorOrBackPointerOffset));
+  bind(&loop);
+  JumpIfSmi(result, &done);
+  CompareObjectType(result, temp, temp2, MAP_TYPE);
+  b(ne, &done);
+  ldr(result, FieldMemOperand(result, Map::kConstructorOrBackPointerOffset));
+  b(&loop);
+  bind(&done);
+}
+
+
 void MacroAssembler::TryGetFunctionPrototype(Register function,
                                              Register result,
                                              Register scratch,
@@ -2345,7 +2359,7 @@ void MacroAssembler::TryGetFunctionPrototype(Register function,
     // Non-instance prototype: Fetch prototype from constructor field
     // in initial map.
     bind(&non_instance);
-    ldr(result, FieldMemOperand(result, Map::kConstructorOffset));
+    GetMapConstructor(result, result, scratch, ip);
   }
 
   // All done.