Implement try/catch without finally, and without type checks.

frog/leg/typechecker.dart

 // Copyright (c) 2012, 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.
 
 class TypeCheckerTask extends CompilerTask {
   TypeCheckerTask(Compiler compiler) : super(compiler);
   String get name() => "Type checker";
 
   void check(Node tree, TreeElements elements) {
     measure(() {
@@ skipping 588 matching lines @@
 
   visitNamedArgument(NamedArgument node) {
     fail(node, 'named argument not implemented');
   }
 
   visitSwitchStatement(SwitchStatement node) {
     compiler.unimplemented('visitSwitchStatement', node: node);
   }
 
   visitTryStatement(TryStatement node) {
-    compiler.unimplemented('visitTryStatement', node: node);
+    fail(node, 'unimplemented');
   }
 
   visitScriptTag(ScriptTag node) {
     compiler.unimplemented('visitScriptTag', node: node);
   }
 
   visitCatchBlock(CatchBlock node) {
     compiler.unimplemented('visitCatchBlock', node: node);
   }
 
   visitTypedef(Typedef node) {
     compiler.unimplemented('visitTypedef', node: node);
   }
 }