[ios] Moves find-in-page code out of Tab and into FindTabHelper.

ios/chrome/browser/find_in_page/find_tab_helper.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_FIND_IN_PAGE_FIND_TAB_HELPER_H_
+#define IOS_CHROME_BROWSER_FIND_IN_PAGE_FIND_TAB_HELPER_H_
+
+#include "base/macros.h"
+#include "ios/web/public/web_state/web_state_observer.h"
+#import "ios/web/public/web_state/web_state_user_data.h"
+
+@class FindInPageController;
+@protocol FindInPageControllerDelegate;
+
+// Adds support for the "Find in page" feature.
+class FindTabHelper : public web::WebStateObserver,
+                      public web::WebStateUserData<FindTabHelper> {
+ public:
+  // Creates a FindTabHelper and attaches it to the given |web_state|.
+  // |controller_delegate| can be nil.
+  static void CreateForWebState(
+      web::WebState* web_state,
+      id<FindInPageControllerDelegate> controller_delegate);
+
+  // Returns the find in page controller.
+  FindInPageController* GetController();
+
+ private:
+  FindTabHelper(web::WebState* web_state,
+                id<FindInPageControllerDelegate> controller_delegate);
+  ~FindTabHelper() override;
+
+  // web::WebStateObserver.
+  void NavigationItemCommitted(
+      const web::LoadCommittedDetails& load_details) override;
+  void WebStateDestroyed() override;
+
+  // The ObjC find in page controller.
+  FindInPageController* controller_;
+
+  DISALLOW_COPY_AND_ASSIGN(FindTabHelper);
+};
+
+#endif  // IOS_CHROME_BROWSER_FIND_IN_PAGE_FIND_TAB_HELPER_H_