Add empty SearchEngineTabHelper.

Add SearchEngineTabHelper without any functionality. This TabHelper will
be the main worker for custom search engines feature.

Bug: 433824
Cq-Include-Trybots: luci.chromium.try:ios-simulator-cronet;luci.chromium.try:ios-simulator-full-configs
Change-Id: Ie18b9237d0f1df52d94ff2c9b4e70b299ab426b1
Reviewed-on: https://chromium-review.googlesource.com/c/1288431
Commit-Queue: Yi Su <mrsuyi@chromium.org>
Reviewed-by: Mark Cogan <marq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600759}

ios/chrome/browser/search_engines/BUILD.gn

@@ -20,6 +20,8 @@ source_set("search_engines") {
   sources = [
     "search_engine_observer_bridge.h",
     "search_engine_observer_bridge.mm",
+    "search_engine_tab_helper.h",
+    "search_engine_tab_helper.mm",
     "search_engines_util.cc",
     "search_engines_util.h",
     "template_url_fetcher_factory.cc",

ios/chrome/browser/search_engines/search_engine_tab_helper.h

+// Copyright 2018 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_SEARCH_ENGINES_SEARCH_ENGINE_TAB_HELPER_H_
+#define IOS_CHROME_BROWSER_SEARCH_ENGINES_SEARCH_ENGINE_TAB_HELPER_H_
+
+#include "base/macros.h"
+#include "base/memory/weak_ptr.h"
+#import "ios/web/public/web_state/web_state_observer.h"
+#import "ios/web/public/web_state/web_state_user_data.h"
+
+namespace web {
+class WebState;
+}  // namespace web
+
+class SearchEngineTabHelper
+    : public web::WebStateObserver,
+      public web::WebStateUserData<SearchEngineTabHelper> {
+ public:
+  ~SearchEngineTabHelper() override;
+
+ private:
+  friend class web::WebStateUserData<SearchEngineTabHelper>;
+
+  explicit SearchEngineTabHelper(web::WebState* web_state);
+
+  // WebStateObserver implementation.
+  void WebStateDestroyed(web::WebState* web_state) override;
+
+  // WebState this tab helper is attached to.
+  web::WebState* web_state_ = nullptr;
+
+  base::WeakPtrFactory<SearchEngineTabHelper> weak_ptr_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(SearchEngineTabHelper);
+};
+
+#endif  // IOS_CHROME_BROWSER_SEARCH_ENGINES_SEARCH_ENGINE_TAB_HELPER_H_

ios/chrome/browser/search_engines/search_engine_tab_helper.mm

+// Copyright 2018 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/search_engines/search_engine_tab_helper.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+DEFINE_WEB_STATE_USER_DATA_KEY(SearchEngineTabHelper);
+
+SearchEngineTabHelper::~SearchEngineTabHelper() {}
+
+SearchEngineTabHelper::SearchEngineTabHelper(web::WebState* web_state)
+    : web_state_(web_state), weak_ptr_factory_(this) {
+  web_state->AddObserver(this);
+}
+
+void SearchEngineTabHelper::WebStateDestroyed(web::WebState* web_state) {
+  web_state->RemoveObserver(this);
+  web_state_ = nullptr;
+}

ios/chrome/browser/tabs/BUILD.gn

@@ -104,6 +104,7 @@ source_set("tabs_internal") {
     "//ios/chrome/browser/prerender",
     "//ios/chrome/browser/reading_list",
     "//ios/chrome/browser/search_engines",
+    "//ios/chrome/browser/search_engines:feature_flags",
     "//ios/chrome/browser/sessions",
     "//ios/chrome/browser/sessions:serialisation",
     "//ios/chrome/browser/snapshots",

ios/chrome/browser/tabs/tab_helper_util.mm

@@ -29,6 +29,8 @@
 #import "ios/chrome/browser/passwords/password_tab_helper.h"
 #include "ios/chrome/browser/reading_list/reading_list_model_factory.h"
 #import "ios/chrome/browser/reading_list/reading_list_web_state_observer.h"
+#import "ios/chrome/browser/search_engines/feature_flags.h"
+#import "ios/chrome/browser/search_engines/search_engine_tab_helper.h"
 #import "ios/chrome/browser/sessions/ios_chrome_session_tab_helper.h"
 #import "ios/chrome/browser/snapshots/snapshot_tab_helper.h"
 #include "ios/chrome/browser/ssl/captive_portal_features.h"
@@ -101,6 +103,10 @@ void AttachTabHelpers(web::WebState* web_state, bool for_prerender) {
     ImageFetchTabHelper::CreateForWebState(web_state);
   }
 
+  if (base::FeatureList::IsEnabled(kCustomSearchEngines)) {
+    SearchEngineTabHelper::CreateForWebState(web_state);
+  }
+
   ReadingListModel* model =
       ReadingListModelFactory::GetForBrowserState(browser_state);
   ReadingListWebStateObserver::CreateForWebState(web_state, model);