dart2js cps: Type casts and related changes to type propagation.

pkg/compiler/lib/src/tree_ir/optimization/statement_rewriter.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 tree_ir.optimization.statement_rewriter;
 
 import 'optimization.dart' show Pass;
 import '../tree_ir_nodes.dart';
 
 /**
@@ skipping 417 matching lines @@
 
   Statement visitThrow(Throw node) {
     node.value = visitExpression(node.value);
     return node;
   }
 
   Statement visitRethrow(Rethrow node) {
     return node;
   }
 
+  Statement visitUnreachable(Unreachable node) {
+    return node;
+  }
+
   Statement visitBreak(Break node) {
     // Redirect through chain of breaks.
     // Note that useCount was accounted for at visitLabeledStatement.
     // Note redirect may return either a Break or Continue statement.
     Jump jump = redirect(node);
     if (jump is Break &&
         jump.target.useCount == 1 &&
         safeForInlining.contains(jump.target)) {
       --jump.target.useCount;
       return visitStatement(jump.target.binding.next);
@@ skipping 464 matching lines @@
 }
 
 /// Result of combining two expressions that do not affect reference counting.
 class GenericCombinedExpressions implements CombinedExpressions {
   Expression combined;
 
   GenericCombinedExpressions(this.combined);
 
   void uncombine() {}
 }