Update call to willShowInstallBannerPrompt to remove implicit conversion

chrome/renderer/chrome_render_frame_observer.cc

Index: chrome/renderer/chrome_render_frame_observer.cc
diff --git a/chrome/renderer/chrome_render_frame_observer.cc b/chrome/renderer/chrome_render_frame_observer.cc
index bcfc00d8a0ebcc9dae35a56eb1b339328acd7552..a67f8fcc2364eb3e2210dafe56eef9f1da58c977 100644
--- a/chrome/renderer/chrome_render_frame_observer.cc
+++ b/chrome/renderer/chrome_render_frame_observer.cc
@@ -198,7 +198,7 @@ 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));