Merge CoreTypes and CoreClasses into CommonElements.

pkg/compiler/lib/src/constant_system_dart.dart

Index: pkg/compiler/lib/src/constant_system_dart.dart
diff --git a/pkg/compiler/lib/src/constant_system_dart.dart b/pkg/compiler/lib/src/constant_system_dart.dart
index e1d468df5e05de6363e5362ab8b0d18fbb56f547..8df511fa19eb250cefa54bbc187cd91ae16eb9de 100644
--- a/pkg/compiler/lib/src/constant_system_dart.dart
+++ b/pkg/compiler/lib/src/constant_system_dart.dart
@@ -446,8 +446,8 @@ class DartConstantSystem extends ConstantSystem {
   @override
   ConstantValue createType(Compiler compiler, DartType type) {
     // TODO(johnniwinther): Change the `Type` type to
-    // `compiler.coreTypes.typeType` and check the backend specific value in
-    // [checkConstMapKeysDontOverrideEquals] in 'members.dart'.
+    // `compiler.commonElements.typeType` and check the backend specific value
+    // in [checkConstMapKeysDontOverrideEquals] in 'members.dart'.
     return new TypeConstantValue(
         type,
         compiler.backend.backendClasses.typeImplementation