Adds mrc instruction to arm simulator, assembler, disassembler.

runtime/vm/assembler_macros_arm.h

Index: runtime/vm/assembler_macros_arm.h
===================================================================
--- runtime/vm/assembler_macros_arm.h	(revision 19404)
+++ runtime/vm/assembler_macros_arm.h	(working copy)
@@ -44,6 +44,10 @@
   static void EnterStubFrame(Assembler* assembler);
   static void LeaveStubFrame(Assembler* assembler);
 
+  // Check whether we have an integer division instruction.
+  // After, rd will be non-zero if we have sdiv and udiv instructions.
+  static void HasDiv(Assembler* assembler, Register rd);

[regis, 2013/03/04 21:54:52]

This method is not necessary. The code testing for this feature should be
executed once in CPUFeatures::InitOnce().

+
   // Instruction pattern from entrypoint is used in dart frame prologs
   // to set up the frame and save a PC which can be used to figure out the
   // RawInstruction object corresponding to the code running in the frame.