Adds mrc instruction to arm simulator, assembler, disassembler.

runtime/vm/simulator_arm.cc

Index: runtime/vm/simulator_arm.cc
===================================================================
--- runtime/vm/simulator_arm.cc	(revision 19404)
+++ runtime/vm/simulator_arm.cc	(working copy)
@@ -2585,6 +2585,14 @@
         UNIMPLEMENTED();
       }
     }
+  } else if (instr->IsMrcIdIsar0()) {
+    // mrc of ID_ISAR0.
+    Register rd = instr->RdField();
+    if (CPUFeatures::integer_division_supported()) {
+      set_register(rd, 0x02100010);  // sim has sdiv, udiv, bkpt and clz.
+    } else {
+      set_register(rd, 0x00100010);  // simulator has only bkpt and clz.
+    }
   } else {
     UNIMPLEMENTED();
   }