Show all mailto: handlers, but dim unavailable ones.

ios/chrome/browser/web/fake_mailto_handler_helpers.mm

 // 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.
 
 #import "ios/chrome/browser/web/fake_mailto_handler_helpers.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
 
 @implementation FakeMailtoHandlerGmailNotInstalled
 - (BOOL)isAvailable {
   return NO;
 }
 @end
 
 @implementation FakeMailtoHandlerGmailInstalled
 - (BOOL)isAvailable {
   return YES;
 }
 @end
 
+@implementation FakeMailtoHandlerForTesting
+- (instancetype)init {
+  return [super initWithName:@"FakeMail" appStoreID:@"12345678"];
+}
+- (BOOL)isAvailable {
+  return NO;
+}
+- (NSString*)beginningScheme {
+  return @"fakemail:/compose?";
+}
+@end
+
 @implementation CountingMailtoURLRewriterObserver
 @synthesize changeCount = _changeCount;
 - (void)rewriterDidChange:(MailtoURLRewriter*)rewriter {
   ++_changeCount;
 }
 @end