IWYU: Removed some unnecessary includes (mailto_handler*)

ios/chrome/browser/web/mailto_handler_gmail.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/mailto_handler_gmail.h"
-#include "base/strings/sys_string_conversions.h"
-#include "url/gurl.h"
-#include "url/url_constants.h"
 
 #import <UIKit/UIKit.h>
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
 
 @implementation MailtoHandlerGmail
 
 - (instancetype)init {
   // Gmail product name is not supposed to be localized.
   self = [super initWithName:@"Gmail" appStoreID:@"422689480"];
   return self;
 }
 
 - (NSString*)beginningScheme {
   return @"googlegmail:/co?";
 }
 
 @end