Adds Compose Email Settings UI for deprecating Native App Launcher

ios/chrome/browser/web/fake_mailto_handler_helpers.mm

Index: ios/chrome/browser/web/fake_mailto_handler_helpers.mm
diff --git a/ios/chrome/browser/web/fake_mailto_handler_helpers.mm b/ios/chrome/browser/web/fake_mailto_handler_helpers.mm
new file mode 100644
index 0000000000000000000000000000000000000000..c370dfec3dfb7af5515a88f2c27ffb25c368a11a
--- /dev/null
+++ b/ios/chrome/browser/web/fake_mailto_handler_helpers.mm
@@ -0,0 +1,24 @@
+// 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"
+
+@implementation FakeMailtoHandlerGmailNotInstalled
+- (BOOL)isAvailable {
+  return NO;
+}
+@end
+
+@implementation FakeMailtoHandlerGmailInstalled
+- (BOOL)isAvailable {
+  return YES;
+}
+@end
+
+@implementation CountingMailtoURLRewriterObserver
+@synthesize changeCount = _changeCount;
+- (void)rewriterDidChange:(MailtoURLRewriter*)rewriter {
+  ++_changeCount;
+}
+@end