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

pkg/compiler/lib/src/tree_ir/tree_ir_tracer.dart

Index: pkg/compiler/lib/src/tree_ir/tree_ir_tracer.dart
diff --git a/pkg/compiler/lib/src/tree_ir/tree_ir_tracer.dart b/pkg/compiler/lib/src/tree_ir/tree_ir_tracer.dart
index acf3133eeb484e4f7d3d76b745543ef7992a788f..cb1659b7688752adac610386e3bb7b72f693026b 100644
--- a/pkg/compiler/lib/src/tree_ir/tree_ir_tracer.dart
+++ b/pkg/compiler/lib/src/tree_ir/tree_ir_tracer.dart
@@ -86,6 +86,10 @@ class BlockCollector extends StatementVisitor {
     _addStatement(node);
   }
 
+  visitUnreachable(Unreachable node) {
+    _addStatement(node);
+  }
+
   visitBreak(Break node) {
     _addStatement(node);
     blocks.last.addEdgeTo(breakTargets[node.target]);
@@ -261,6 +265,10 @@ class TreeTracer extends TracerUtil with StatementVisitor {
     printStatement(null, "rethrow");
   }
 
+  visitUnreachable(Unreachable node) {
+    printStatement(null, "unreachable");
+  }
+
   visitBreak(Break node) {
     printStatement(null, "break ${collector.breakTargets[node.target].name}");
   }