Add Chain.foldFrames to pkg/stack_trace.

pkg/stack_trace/test/chain_test.dart

 // Copyright (c) 2013, 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 chain_test;
 
 import 'dart:async';
 
 import 'package:path/path.dart' as p;
 import 'package:stack_trace/stack_trace.dart';
@@ skipping 369 matching lines @@
       ]);
 
       expect(chain.terse.toString(), equals(
           '$userSlashCode 10:11  Foo.bar\n'
           'dart:core             Bar.baz\n'
           '===== asynchronous gap ===========================\n'
           '$userSlashCode 10:11  Foo.bar\n'
           'dart:core             Bar.baz\n'));
     });
 
-    test("doesn't return in an empty chain", () {
+    test("doesn't return an empty chain", () {
       var chain = new Chain([
         new Trace.parse(
             'dart:core 10:11                             Foo.bar\n'
             'package:stack_trace/stack_trace.dart 10:11  Bar.baz\n'
             'dart:core 10:11                             Zip.zap'),
         new Trace.parse(
             'dart:core 10:11                             A.b\n'
             'package:stack_trace/stack_trace.dart 10:11  C.d\n'
             'dart:core 10:11                             E.f')
       ]);
 
       expect(chain.terse.toString(), equals('dart:core  E.f\n'));
     });
   });
 
+  group('Chain.foldFrames', () {
+    test('folds each trace', () {
+      var chain = new Chain([
+        new Trace.parse(
+            'a.dart 10:11  Foo.bar\n'
+            'a.dart 10:11  Bar.baz\n'
+            'b.dart 10:11  Bang.qux\n'
+            'a.dart 10:11  Zip.zap\n'
+            'a.dart 10:11  Zop.zoop'),
+        new Trace.parse(
+            'a.dart 10:11  Foo.bar\n'
+            'a.dart 10:11  Bar.baz\n'
+            'a.dart 10:11  Bang.qux\n'
+            'a.dart 10:11  Zip.zap\n'
+            'b.dart 10:11  Zop.zoop')
+      ]);
+
+      var folded = chain.foldFrames((frame) => frame.library == 'a.dart');
+      expect(folded.toString(), equals(
+          'a.dart 10:11  Bar.baz\n'
+          'b.dart 10:11  Bang.qux\n'
+          'a.dart 10:11  Zop.zoop\n'
+          '===== asynchronous gap ===========================\n'
+          'a.dart 10:11  Zip.zap\n'
+          'b.dart 10:11  Zop.zoop\n'));
+    });
+
+    test('eliminates completely-folded traces', () {
+      var chain = new Chain([
+        new Trace.parse(
+            'a.dart 10:11  Foo.bar\n'
+            'b.dart 10:11  Bang.qux'),
+        new Trace.parse(
+            'a.dart 10:11  Foo.bar\n'
+            'a.dart 10:11  Bang.qux'),
+        new Trace.parse(
+            'a.dart 10:11  Zip.zap\n'
+            'b.dart 10:11  Zop.zoop')
+      ]);
+
+      var folded = chain.foldFrames((frame) => frame.library == 'a.dart');
+      expect(folded.toString(), equals(
+          'a.dart 10:11  Foo.bar\n'
+          'b.dart 10:11  Bang.qux\n'
+          '===== asynchronous gap ===========================\n'
+          'a.dart 10:11  Zip.zap\n'
+          'b.dart 10:11  Zop.zoop\n'));
+    });
+
+    test("doesn't return an empty trace", () {
+      var chain = new Chain([
+        new Trace.parse(
+            'a.dart 10:11  Foo.bar\n'
+            'a.dart 10:11  Bang.qux')
+      ]);
+
+      var folded = chain.foldFrames((frame) => frame.library == 'a.dart');
+      expect(folded.toString(), equals('a.dart 10:11  Bang.qux\n'));
+    });
+  });
+
   test('Chain.toTrace eliminates asynchronous gaps', () {
     var trace = new Chain([
       new Trace.parse(
           'user/code.dart 10:11  Foo.bar\n'
           'dart:core 10:11       Bar.baz'),
       new Trace.parse(
           'user/code.dart 10:11  Foo.bar\n'
           'dart:core 10:11       Bar.baz')
     ]).toTrace();
 
@@ skipping 210 matching lines @@
 ///
 /// [callback] is expected to throw the string `"error"`.
 Future<Chain> captureFuture(callback()) {
   var completer = new Completer<Chain>();
   Chain.capture(callback, onError: (error, chain) {
     expect(error, equals('error'));
     completer.complete(chain);
   });
   return completer.future;
 }