Plumbing from WebPresentationClient to the Presentation Mojo service for

content/common/presentation/presentation_service.mojom

Index: content/common/presentation/presentation_service.mojom
diff --git a/content/common/presentation/presentation_service.mojom b/content/common/presentation/presentation_service.mojom
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@@ -0,0 +1,15 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+module presentation;
+
+interface PresentationService {
+  // Called when there's at least one listener for the |availablechange| event
+  // and the client is ready to process the result. To get the subsequent event

[mark a. foltz, 2015/01/27 21:56:09]

I didn't quite follow the second sentence.  Should the client always call this
method twice and ignore the first result?  Or should it just call the method
repeatedly to get the latest availability status?

[whywhat, 2015/01/28 01:52:37]

Call the method repeatedly. Updated the wording.

+  // the client has to call the method again when it's ready.
+  // Might start the presentation screens discovery. The discovery might be

[mark a. foltz, 2015/01/27 21:56:09]

May start discovery of presentation screens.  The implementation may stop
discovery once there are no active calls to GetScreenAvailability.

[whywhat, 2015/01/28 01:52:37]

I actually introduced an explicit OnScreenAvailabilityListenerRemoved() method
to help stop discovery faster. See our Mojo service document.

+  // stopped by the service implementation if there's no active calls to get
+  // screens availability at the moment.
+  GetScreenAvailability() => (bool available);
+};