dart2js cps: Compute intercepted classes in optimize_interceptors.

pkg/compiler/lib/src/cps_ir/optimizers.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library dart2js.cps_ir.optimizers;
 
 import 'cps_ir_nodes.dart';
 import '../constants/values.dart';
+import '../common/names.dart';
+import '../universe/selector.dart';
 
 export 'type_propagation.dart' show TypePropagator;
 export 'scalar_replacement.dart' show ScalarReplacer;
 export 'redundant_phi.dart' show RedundantPhiEliminator;
 export 'redundant_join.dart' show RedundantJoinEliminator;
 export 'shrinking_reductions.dart' show ShrinkingReducer;
 export 'mutable_ssa.dart' show MutableVariableEliminator;
 export 'insert_refinements.dart' show InsertRefinements;
 export 'update_refinements.dart' show UpdateRefinements;
 export 'redundant_refinement.dart' show RedundantRefinementEliminator;
@@ skipping 25 matching lines @@
       value is StringConstantValue && value.primitiveValue.isEmpty;
 }
 
 /// Returns true if [value] satisfies a branching condition with the
 /// given strictness.
 ///
 /// For non-strict, this is the opposite of [isFalsyConstant].
 bool isTruthyConstant(ConstantValue value, {bool strict: false}) {
   return strict ? value.isTrue : !isFalsyConstant(value);
 }
+
+/// Selector that do not throw when invoked on the null class.
+final List<Selector> selectorsOnNull = <Selector>[
+    Selectors.equals, Selectors.hashCode_, Selectors.runtimeType_,
+    Selectors.toString_];