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

src/arm64/macro-assembler-arm64.h

 // Copyright 2013 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_ARM64_MACRO_ASSEMBLER_ARM64_H_
 #define V8_ARM64_MACRO_ASSEMBLER_ARM64_H_
 
 #include <vector>
 
 #include "src/bailout-reason.h"
@@ skipping 1360 matching lines @@
 
   // 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.
   enum BoundFunctionAction {
     kMissOnBoundFunction,
     kDontMissOnBoundFunction
   };
 
+  // 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);
+
   void TryGetFunctionPrototype(Register function,
                                Register result,
                                Register scratch,
                                Label* miss,
                                BoundFunctionAction action =
                                  kDontMissOnBoundFunction);
 
   // Compare object type for heap object.  heap_object contains a non-Smi
   // whose object type should be compared with the given type.  This both
   // sets the flags and leaves the object type in the type_reg register.
@@ skipping 926 matching lines @@
 #error "Unsupported option"
 #define CODE_COVERAGE_STRINGIFY(x) #x
 #define CODE_COVERAGE_TOSTRING(x) CODE_COVERAGE_STRINGIFY(x)
 #define __FILE_LINE__ __FILE__ ":" CODE_COVERAGE_TOSTRING(__LINE__)
 #define ACCESS_MASM(masm) masm->stop(__FILE_LINE__); masm->
 #else
 #define ACCESS_MASM(masm) masm->
 #endif
 
 #endif  // V8_ARM64_MACRO_ASSEMBLER_ARM64_H_