[AppBanner] Blink implementation of an event when an install banner is shown.

Source/web/WebLocalFrameImpl.cpp

Index: Source/web/WebLocalFrameImpl.cpp
diff --git a/Source/web/WebLocalFrameImpl.cpp b/Source/web/WebLocalFrameImpl.cpp
index 657ef0749a48fe71afbb43b7a7abc8ee5a761b61..e6a1c2a2164163bece4edb9320396b058e828e01 100644
--- a/Source/web/WebLocalFrameImpl.cpp
+++ b/Source/web/WebLocalFrameImpl.cpp
@@ -149,6 +149,7 @@
 #include "core/page/PrintContext.h"
 #include "core/timing/DOMWindowPerformance.h"
 #include "core/timing/Performance.h"
+#include "modules/app_banner/AppBannerController.h"
 #include "modules/geolocation/GeolocationController.h"
 #include "modules/notifications/NotificationPermissionClient.h"
 #include "modules/presentation/PresentationController.h"
@@ -1946,6 +1947,14 @@ void WebLocalFrameImpl::sendOrientationChangeEvent()
         frame()->localDOMWindow()->sendOrientationChangeEvent();
 }
 
+void WebLocalFrameImpl::willShowInstallBannerPrompt(const WebString& platform, WebAppBannerPromptReply* reply)
+{
+    if (!RuntimeEnabledFeatures::appBannerEnabled() || !frame())
+        return;
+
+    AppBannerController::willShowInstallBannerPrompt(frame(), platform, reply);
+}
+
 void WebLocalFrameImpl::willDetachParent()
 {
     // Do not expect string scoping results from any frames that got detached