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

src/arm/macro-assembler-arm.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_ARM_MACRO_ASSEMBLER_ARM_H_
 #define V8_ARM_MACRO_ASSEMBLER_ARM_H_
 
 #include "src/assembler.h"
 #include "src/bailout-reason.h"
 #include "src/frames.h"
@@ skipping 793 matching lines @@
   // Initialize fields with filler values.  Fields starting at |start_offset|
   // not including end_offset are overwritten with the value in |filler|.  At
   // the end the loop, |start_offset| takes the value of |end_offset|.
   void InitializeFieldsWithFiller(Register start_offset,
                                   Register end_offset,
                                   Register filler);
 
   // ---------------------------------------------------------------------------
   // Support functions.
 
+  // Machine code version of Map::GetConstructor().
+  // |temp| holds |result|'s map when done, and |temp2| its instance type.
+  void GetMapConstructor(Register result, Register map, Register temp,
+                         Register temp2);
+
   // Try to get function prototype of a function and puts the value in
   // the result register. Checks that the function really is a
   // function and jumps to the miss label if the fast checks fail. The
   // function register will be untouched; the other registers may be
   // clobbered.
   void TryGetFunctionPrototype(Register function,
                                Register result,
                                Register scratch,
                                Label* miss,
                                bool miss_on_bound_function = false);
@@ skipping 720 matching lines @@
 #define __FILE_LINE__ __FILE__ ":" CODE_COVERAGE_TOSTRING(__LINE__)
 #define ACCESS_MASM(masm) masm->stop(__FILE_LINE__); masm->
 #else
 #define ACCESS_MASM(masm) masm->
 #endif
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_ARM_MACRO_ASSEMBLER_ARM_H_