Stop using deprecated throws matcher from pkg/test

test/bazel_test.dart

@@ -153,7 +153,7 @@ void main() {
         expect(
             () =>
                 config.outputPathFor(Uri.parse('a/b/c/quux.proto'), '.pb.dart'),
-            throws);
+            throwsArgumentError);
       });
     });
 
@@ -198,7 +198,9 @@ void main() {
       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, '.pb.dart'), throws);
+        expect(
+            () => config.resolveImport(target, source, '.pb.dart'),
+            throwsA(startsWith('ERROR: cannot generate import for')));
       });
     });
   });

test/extension_test.dart

@@ -122,7 +122,7 @@ void main() {
     expect(() {
       message.addExtension(
           Unittest.repeatedNestedMessageExtension, new TestAllTypes());
-    }, throws); // TypeError
+    }, throwsATypeError);
   });
 
   test('throws if an enum extension is set to a bad value', () {
@@ -139,7 +139,7 @@ void main() {
     expect(() {
       message.addExtension(
           Unittest.repeatedForeignEnumExtension, TestAllTypes_NestedEnum.FOO);
-    }, throws); // TypeError
+    }, throwsATypeError);
   });
 
   test('can extend a message with a message field with a different type', () {

test/repeated_field_test.dart

@@ -8,6 +8,7 @@ library repeated_field_test;
 import 'package:test/test.dart';
 
 import '../out/protos/google/protobuf/unittest.pb.dart';
+import 'test_util.dart';
 
 // Suppress an analyzer warning for a deliberate type mismatch.
 cast(x) => x;
@@ -20,7 +21,7 @@ void main() {
 
     expect(() {
       TestAllTypes.$checkItem(cast(new TestAllTypes_NestedMessage()));
-    }, throws);
+    }, throwsATypeError);
   });
 
   test("checkItems works for groups", () {
@@ -31,7 +32,7 @@ void main() {
     expect(() {
       TestAllTypes_RepeatedGroup
           .$checkItem(cast(new TestAllTypes_OptionalGroup()));
-    }, throws);
+    }, throwsATypeError);
   });
 
   test("checkItems works for enums", () {
@@ -41,7 +42,7 @@ void main() {
 
     expect(() {
       TestAllTypes_NestedEnum.$checkItem(cast(ForeignEnum.FOREIGN_FOO));
-    }, throws);
+    }, throwsATypeError);
   });
 
   test("check properties are initialized for repeated fields", () {

test/test_util.dart

@@ -11,6 +11,8 @@ import 'package:test/test.dart';
 import '../out/protos/google/protobuf/unittest_import.pb.dart';
 import '../out/protos/google/protobuf/unittest.pb.dart';
 
+final Matcher throwsATypeError = throwsA(new isInstanceOf<TypeError>());
+
 Int64 make64(lo, [hi = null]) {
   if (hi == null) hi = lo < 0 ? -1 : 0;
   return new Int64.fromInts(hi, lo);