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

src/arm/macro-assembler-arm.h

Index: src/arm/macro-assembler-arm.h
diff --git a/src/arm/macro-assembler-arm.h b/src/arm/macro-assembler-arm.h
index 5de013e27071ddf343cf514dd329e85ec0fc7f2e..15a84b775a93403d480295ce3c196f3616f3f178 100644
--- a/src/arm/macro-assembler-arm.h
+++ b/src/arm/macro-assembler-arm.h
@@ -811,6 +811,11 @@ class MacroAssembler: public Assembler {
   // ---------------------------------------------------------------------------
   // 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