Add hooks for BeforeInstallPromptEvent to be redispatched.

public/platform/modules/app_banner/WebAppBannerClient.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 WebAppBannerClient_h
 #define WebAppBannerClient_h
 
 #include "public/platform/WebCallbacks.h"
 #include "public/platform/modules/app_banner/WebAppBannerPromptResult.h"
 
 namespace blink {
 
 using WebAppBannerCallbacks = WebCallbacks<WebAppBannerPromptResult, void>;
 
 class WebAppBannerClient {
 public:
     virtual ~WebAppBannerClient() { }
 
     // Ownership of the callbacks is transferred to the client.
     virtual void registerBannerCallbacks(int requestId, WebAppBannerCallbacks*) = 0;
+
+    // Tell the client that the event is to be redispatched.
+    //
+    // TODO(dominickn) This method should be pure virtual. However, making it
+    // pure virtual causes compilation failures in tests. This is because the
+    // tests instantiate an AppBannerClient, which lives in the Chromium
+    // repository and inherits from this class. Once AppBannerClient has been
+    // updated to override this method, it will be made pure virtual. For now,
+    // it has a dummy do-nothing implementation.

[mlamouri (slow - plz ping), 2015/06/06 21:40:55]

nit: remove the comment. Not having the function pure virtual isn't a problem.
It's fairly common for Blink interfaces.
Alternatively, just leave a one-liner like "TODO(dominickn) make the method pure
virtual when implemented by Chromium."

+    virtual void resolveEventRedispatch(int requestId) { }
 };
 
 } // namespace blink
 
 #endif // WebAppBannerClient_h