Implemented FormResubmissionTabHelper.

ios/chrome/browser/web/form_resubmission_tab_helper.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/form_resubmission_tab_helper.h"
+
+#import "ios/chrome/browser/ui/alert_coordinator/form_resubmission_coordinator.h"
+#import "ios/chrome/browser/ui/util/top_view_controller.h"
+
+DEFINE_WEB_STATE_USER_DATA_KEY(FormResubmissionTabHelper);
+
+FormResubmissionTabHelper::FormResubmissionTabHelper(web::WebState* web_state)
+    : web::WebStateObserver(web_state) {}
+
+FormResubmissionTabHelper::~FormResubmissionTabHelper() = default;
+
+void FormResubmissionTabHelper::PresentFormResubmissionDialog(
+    CGPoint location,
+    const base::Callback<void(bool)>& callback) {
+  UIViewController* top_controller =

[marq (ping after 24h), 2017/01/18 11:54:19]

I'm fine with this as a refactoring step, but this isn't the approach I want to
take for the new architecture. 

[Eugene But (OOO till 7-30), 2017/01/18 16:13:24]

With my next refactoring step, PresentFormResubmissionDialog call will be moved
to BVC. Do you want me to pass BVC as |baseViewController|?

+      top_view_controller::TopPresentedViewControllerFrom(
+          [UIApplication sharedApplication].keyWindow.rootViewController);
+
+  base::Callback<void(bool)> local_callback(callback);
+  coordinator_.reset([[FormResubmissionCoordinator alloc]
+      initWithBaseViewController:top_controller
+                  dialogLocation:location
+                        webState:web_state()
+               completionHandler:^(BOOL should_continue) {
+                 local_callback.Run(should_continue);
+               }]);
+  [coordinator_ start];
+}
+
+void FormResubmissionTabHelper::ProvisionalNavigationStarted(const GURL&) {
+  coordinator_.reset();
+}
+
+void FormResubmissionTabHelper::WebStateDestroyed() {
+  coordinator_.reset();
+}