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

pkg/compiler/lib/src/tree_ir/optimization/statement_rewriter.dart

Index: pkg/compiler/lib/src/tree_ir/optimization/statement_rewriter.dart
diff --git a/pkg/compiler/lib/src/tree_ir/optimization/statement_rewriter.dart b/pkg/compiler/lib/src/tree_ir/optimization/statement_rewriter.dart
index 691e206adfad569c27630d3e1cb4b29f5f85bf1f..27638c40409bb44c24ab51d8054a0529a0fad51f 100644
--- a/pkg/compiler/lib/src/tree_ir/optimization/statement_rewriter.dart
+++ b/pkg/compiler/lib/src/tree_ir/optimization/statement_rewriter.dart
@@ -435,6 +435,10 @@ class StatementRewriter extends Transformer implements Pass {
     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.