[Presentation API] Adds close method to Presentation session.

public/platform/modules/presentation/WebPresentationClient.h

Index: public/platform/modules/presentation/WebPresentationClient.h
diff --git a/public/platform/modules/presentation/WebPresentationClient.h b/public/platform/modules/presentation/WebPresentationClient.h
index f11b22ff5204ab0f86ee172e6226831e079fc184..ed4eea8d59f533d4a9522278412deef51b380d50 100644
--- a/public/platform/modules/presentation/WebPresentationClient.h
+++ b/public/platform/modules/presentation/WebPresentationClient.h
@@ -6,6 +6,7 @@
 #define WebPresentationClient_h
 
 #include "public/platform/WebCallbacks.h"
+#include "public/platform/WebCommon.h"
 
 namespace blink {
 
@@ -35,9 +36,16 @@ public:
     // The ownership of the |callbacks| argument is transferred to the embedder.
     virtual void startSession(const WebString& presentationUrl, const WebString& presentationId, WebPresentationSessionClientCallbacks*) = 0;
 
-    // Called when the frame request to start a new session.
+    // Called when the frame request to join an existing session.
     // The ownership of the |callbacks| argument is transferred to the embedder.
     virtual void joinSession(const WebString& presentationUrl, const WebString& presentationId, WebPresentationSessionClientCallbacks*) = 0;
+
+    // Called when the frame request to close an existing session.

[whywhat, 2015/03/17 23:35:19]

nit: I think I missed s at the end of the request in the comments above. Could
you s/request/requests, please?

[haibinlu, 2015/03/18 00:58:23]

Done.

+    virtual void closeSession(const WebString& presentationId)
+    {
+        // TODO(haibinlu): make it pure virtual once Chromium has the implementation.

[whywhat, 2015/03/17 23:35:19]

nit: ditto re 80 chars

[haibinlu, 2015/03/18 00:58:23]

Done.

+        BLINK_ASSERT_NOT_REACHED();
+    }
 };
 
 } // namespace blink