[PresentationAPI] Make WebPresentationClient.sendString and sendArrayBuffer methods pure virtual.

public/platform/modules/presentation/WebPresentationClient.h

 // 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 WebPresentationClient_h
 #define WebPresentationClient_h
 
 #include "public/platform/WebCallbacks.h"
 #include "public/platform/WebCommon.h"
 
@@ skipping 22 matching lines @@
     virtual void updateAvailableChangeWatched(bool watched) = 0;
 
     // Called when the frame requests to start a new session.
     // 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 requests 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;
 
-    // TODO(s.singapati): Make below send methods pure virtual once Chromium has the implementation.
     // Called when the frame requests to send String message to an existing session.
-    virtual void sendString(const WebString& presentationUrl, const WebString& presentationId, const WebString& message)
-    {
-        BLINK_ASSERT_NOT_REACHED();
-    }
+    virtual void sendString(const WebString& presentationUrl, const WebString& presentationId, const WebString& message) = 0;
+
     // Called when the frame requests to send ArrayBuffer/View data to an existing session.
-    virtual void sendArrayBuffer(const WebString& presentationUrl, const WebString& presentationId, const uint8_t* data, size_t length)
-    {
-        BLINK_ASSERT_NOT_REACHED();
-    }
+    virtual void sendArrayBuffer(const WebString& presentationUrl, const WebString& presentationId, const uint8_t* data, size_t length) = 0;
 
     // Called when the frame requests to close an existing session.
     virtual void closeSession(const WebString& url, const WebString& presentationId) = 0;
 };
 
 } // namespace blink
 
 #endif // WebPresentationClient_h