Update headings to use sentence case.

pkg/scheduled_test/lib/scheduled_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.
 
 // TODO(nweiz): Add support for calling [schedule] while the schedule is already
 // running.
 // TODO(nweiz): Port the non-Pub-specific scheduled test libraries from Pub.
 /// A package for writing readable tests of asynchronous behavior.
 ///
 /// ## Installing ##
@@ skipping 31 matching lines @@
 ///
 ///         schedule(() {
 ///           return new File("output.txt").readAsString().then((contents) {
 ///             // The normal unittest matchers can still be used.
 ///             expect(contents, equals("contents"));
 ///           });
 ///         });
 ///       });
 ///     }
 ///
-/// ## Setting Up and Tearing Down
+/// ## Setting up and tearing down
 ///
 /// The `scheduled_test` package defines its own [setUp] method that works just
 /// like the one in `unittest`. Tasks can be scheduled in [setUp]; they'll be
 /// run before the tasks scheduled by tests in that group. [currentSchedule] is
 /// also set in the [setUp] callback.
 ///
 /// This package doesn't have an explicit `tearDown` method. Instead, the
 /// [currentSchedule.onComplete] and [currentSchedule.onException] task queues
 /// can have tasks scheduled during [setUp]. For example:
 ///
 ///     import 'package:scheduled_test/scheduled_test.dart';
 ///
 ///     void main() {
 ///       var tempDir;
 ///       setUp(() {
 ///         schedule(() {
 ///           return createTempDir().then((dir) {
 ///             tempDir = dir;
 ///           });
 ///         });
 ///
 ///         currentSchedule.onComplete.schedule(() => deleteDir(tempDir));
 ///       });
 ///
 ///       // ...
 ///     }
 ///
-/// ## Passing Values Between Tasks
+/// ## Passing values between tasks
 ///
 /// It's often useful to use values computed in one task in other tasks that are
 /// scheduled afterwards. There are two ways to do this. The most
 /// straightforward is just to define a local variable and assign to it. For
 /// example:
 ///
 ///     import 'package:scheduled_test/scheduled_test.dart';
 ///
 ///     void main() {
 ///       test('computeValue returns 12', () {
@@ skipping 277 matching lines @@
 /// [description] provides an optional description of the future, which is
 /// used when generating error messages.
 Future wrapFuture(Future future, [String description]) {
   if (currentSchedule == null) {
     throw new StateError("Unexpected call to wrapFuture with no current "
         "schedule.");
   }
 
   return currentSchedule.wrapFuture(future, description);
 }