Fix all strong mode warnings in protoc-plugin

test/bazel_test.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 bazel_test;
 
 import 'package:protoc_plugin/bazel.dart';
 import 'package:test/test.dart';
 
 void main() {
   group('BazelOptionParser', () {
     var optionParser;
-    var packages;
+    Map<String, BazelPackage> packages;
     var errors;
 
     setUp(() {
       packages = {};
       optionParser = new BazelOptionParser(packages);
       errors = [];
     });
 
     _onError(String message) {
       errors.add(message);
@@ skipping 80 matching lines @@
       expect(packages['b'].name, 'a');
       expect(packages['b'].input_root, 'b');
       expect(packages['b'].output_root, 'c');
       expect(packages['d/e/f'].name, 'c');
       expect(packages['d/e/f'].input_root, 'd/e/f');
       expect(packages['d/e/f'].output_root, 'g/h');
     });
   });
 
   group('BazelOutputConfiguration', () {
-    var packages;
+    Map<String, BazelPackage> packages;
     var config;
 
     setUp(() {
       packages = {
         'foo/bar': new BazelPackage('a.b.c', 'foo/bar', 'baz/flob'),
         'foo/bar/baz': new BazelPackage('d.e.f', 'foo/bar/baz', 'baz/flob/foo'),
         'wibble/wobble':
             new BazelPackage('wibble.wobble', 'wibble/wobble', 'womble/wumble'),
       };
       config = new BazelOutputConfiguration(packages);
@@ skipping 65 matching lines @@
       });
 
       test('should throw if target is in unknown package', () {
         var target = Uri.parse('flob/flub/quux.proto');
         var source = Uri.parse('foo/bar/baz.proto');
         expect(() => config.resolveImport(target, source), throws);
       });
     });
   });
 }