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

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 a5a7f229820a7cf5e042641bf29bec8833347436..15e4d6e15845395d0046f36c3c35d3e8381763bf 100644
--- a/public/platform/modules/presentation/WebPresentationClient.h
+++ b/public/platform/modules/presentation/WebPresentationClient.h
@@ -40,17 +40,11 @@ public:
     // 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;