Update call to willShowInstallBannerPrompt to remove implicit conversion

chrome/renderer/chrome_render_frame_observer.cc

 // Copyright 2013 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.
 
 #include "chrome/renderer/chrome_render_frame_observer.h"
 
 #include <limits>
 #include <string>
 #include <vector>
 
@@ skipping 180 matching lines @@
                   "tampering. Get a valid SSL certificate before"
                   " releasing your website to the public.")));
     }
   }
 }
 
 void ChromeRenderFrameObserver::OnAppBannerPromptRequest(
     int request_id, const std::string& platform) {
   blink::WebAppBannerPromptReply reply = blink::WebAppBannerPromptReply::None;
   render_frame()->GetWebFrame()->willShowInstallBannerPrompt(
-      base::UTF8ToUTF16(platform), &reply);
+      blink::WebString(base::UTF8ToUTF16(platform)), &reply);
 
   Send(new ChromeViewHostMsg_AppBannerPromptReply(
       routing_id(), request_id, reply));
 }