Fix some crashes.

pkg/front_end/lib/src/fasta/fasta.dart

 // Copyright (c) 2016, 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 fasta;
 
 import 'dart:async' show Future;
 
 import 'dart:convert' show JSON;
 
@@ skipping 147 matching lines @@
           formatUnexpected(fileName, -1, "No such file."));
     }
     if (!await new Directory.fromUri(patchedSdk).exists()) {
       return new CompilationResult.error(
           formatUnexpected(patchedSdk, -1, "Patched sdk directory not found."));
     }
 
     Target target = getTarget("vm", new TargetFlags(strongMode: false));
 
     Program program;
-    final uriTranslator = await TranslateUri.parse(null, packages);
-    final Ticker ticker = new Ticker(isVerbose: verbose);
-    final DillTarget dillTarget = new DillTarget(ticker, uriTranslator);
-    dillTarget.read(patchedSdk.resolve('platform.dill'));
-    final KernelTarget kernelTarget =
-        new KernelTarget(dillTarget, uriTranslator);
     try {
+      TranslateUri uriTranslator = await TranslateUri.parse(null, packages);
+      final Ticker ticker = new Ticker(isVerbose: verbose);
+      final DillTarget dillTarget = new DillTarget(ticker, uriTranslator);
+      dillTarget.read(patchedSdk.resolve('platform.dill'));
+      final KernelTarget kernelTarget =
+          new KernelTarget(dillTarget, uriTranslator);
       kernelTarget.read(fileName);
       await dillTarget.writeOutline(null);
       program = await kernelTarget.writeOutline(null);
       program = await kernelTarget.writeProgram(null);
       if (kernelTarget.errors.isNotEmpty) {
         return new CompilationResult.errors(kernelTarget.errors
             .map((err) => err.toString())
             .toList(growable: false));
       }
     } on InputError catch (e) {
@@ skipping 59 matching lines @@
   final BytesBuilder builder = new BytesBuilder();
 
   void add(List<int> data) {
     builder.add(data);
   }
 
   void close() {
     // Nothing to do.
   }
 }