Reapply 'Add runtimeType() to Object which returns canonicalized instances of Type'.

lib/compiler/implementation/compiler.dart

Index: lib/compiler/implementation/compiler.dart
diff --git a/lib/compiler/implementation/compiler.dart b/lib/compiler/implementation/compiler.dart
index f533623192b54941161f181c274d2b44964b40ef..40d7b97c40c0c68ea1385cd7c99d8766951e3198 100644
--- a/lib/compiler/implementation/compiler.dart
+++ b/lib/compiler/implementation/compiler.dart
@@ -165,9 +165,11 @@ class Compiler implements DiagnosticListener {
   static const SourceString MAIN = const SourceString('main');
   static const SourceString CALL_OPERATOR_NAME = const SourceString('call');
   static const SourceString NO_SUCH_METHOD = const SourceString('noSuchMethod');
+  static const SourceString RUNTIME_TYPE = const SourceString('runtimeType');
   static const SourceString START_ROOT_ISOLATE =
       const SourceString('startRootIsolate');
   bool enabledNoSuchMethod = false;
+  bool enabledRuntimeType = false;
 
   Stopwatch progress;