Recognize and optimize a.runtimeType == b.runtimeType pattern.

runtime/lib/integers.dart

Index: runtime/lib/integers.dart
diff --git a/runtime/lib/integers.dart b/runtime/lib/integers.dart
index 0c5b11985bad5dd6648392883097aec8ee5f26cc..f465e3bd6bc27a8ccc00482e54e26281ae2ad725 100644
--- a/runtime/lib/integers.dart
+++ b/runtime/lib/integers.dart
@@ -6,8 +6,6 @@ abstract class _IntegerImplementation {
   // The Dart class _Bigint extending _IntegerImplementation requires a
   // default constructor.
 
-  Type get runtimeType => int;
-
   num operator +(num other) {
     var result = other._addFromInteger(this);
     if (result != null) return result;