[PresentationAPI] Added/changed public/platform interfaces for start/joinSession

public/platform/modules/presentation/WebPresentationSessionClient.h

Index: public/platform/modules/presentation/WebPresentationSessionClient.h
diff --git a/public/platform/modules/presentation/WebPresentationSessionClient.h b/public/platform/modules/presentation/WebPresentationSessionClient.h
new file mode 100644
index 0000000000000000000000000000000000000000..735ff3cd1602ac6c935cd078eb372a9b416930d3
--- /dev/null
+++ b/public/platform/modules/presentation/WebPresentationSessionClient.h
@@ -0,0 +1,23 @@
+// 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.
+
+#ifndef WebPresentationSessionClient_h
+#define WebPresentationSessionClient_h
+
+#include "public/platform/WebString.h"
+
+namespace blink {
+
+// The implementation the embedder has to provide for the Presentation API to work.
+class WebPresentationSessionClient {
+public:
+    virtual ~WebPresentationSessionClient() { }
+
+    virtual WebString getId() = 0;
+    virtual WebString getUrl() = 0;
+};
+
+} // namespace blink
+
+#endif // WebPresentationSessionClient_h