Show all mailto: handlers, but dim unavailable ones.

ios/chrome/browser/web/fake_mailto_handler_helpers.h

 // Copyright 2017 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 IOS_CHROME_BROWSER_WEB_FAKE_MAILTO_HANLDERS_H_
 #define IOS_CHROME_BROWSER_WEB_FAKE_MAILTO_HANLDERS_H_
 
 #import "ios/chrome/browser/web/mailto_handler.h"
 #import "ios/chrome/browser/web/mailto_handler_gmail.h"
 #import "ios/chrome/browser/web/mailto_url_rewriter.h"
 
 // Test fixtures for faking MailtoHandlerGmail objects that reports whether
 // Gmail app as installed or not.
 
 // Fakes Gmail handler where Gmail app is not installed.
 @interface FakeMailtoHandlerGmailNotInstalled : MailtoHandlerGmail
 @end
 
 // Fakes Gmail handler where Gmail app is installed.
 @interface FakeMailtoHandlerGmailInstalled : MailtoHandlerGmail
 @end
 
+// Fake mailto: handler
+@interface FakeMailtoHandlerForTesting : MailtoHandler
+@end
+
 // An observer object that counts and reports the number of times it has been
 // called by the MailtoURLRewriter object.
 @interface CountingMailtoURLRewriterObserver
     : NSObject<MailtoURLRewriterObserver>
 // Returns the number of times that observer has been called.
 @property(nonatomic, readonly) int changeCount;
 @end
 
 #endif  // IOS_CHROME_BROWSER_WEB_FAKE_MAILTO_HANLDERS_H_