[ios] TabIdTabHelper

ios/chrome/browser/web/tab_id_tab_helper.mm

Index: ios/chrome/browser/web/tab_id_tab_helper.mm
diff --git a/ios/chrome/browser/web/tab_id_tab_helper.mm b/ios/chrome/browser/web/tab_id_tab_helper.mm
new file mode 100644
index 0000000000000000000000000000000000000000..8fe8aa2cc92cc9c93f29623235df349f74d3a92c
--- /dev/null
+++ b/ios/chrome/browser/web/tab_id_tab_helper.mm
@@ -0,0 +1,35 @@
+// 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/tab_id_tab_helper.h"
+
+#include "base/mac/foundation_util.h"
+#include "base/strings/sys_string_conversions.h"
+#import "ios/web/public/serializable_user_data_manager.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+DEFINE_WEB_STATE_USER_DATA_KEY(TabIDTabHelper);
+
+namespace {
+// The key under which the TabID is stored in the WebState's serializable user
+// data.
+NSString* const kTabIDKey = @"TabID";
+}
+
+TabIDTabHelper::TabIDTabHelper(web::WebState* web_state) {
+  web::SerializableUserDataManager* user_data_manager =
+      web::SerializableUserDataManager::FromWebState(web_state);

[rohitrao (ping after 24h), 2017/06/23 11:10:27]

Is this guaranteed to exist before the TabIDTabHelper is created?

[edchin, 2017/06/23 16:24:21]

The class comment says this:
"// Returns the SerializableUserDataManager instance associated with
  // |web_state|, instantiating one if necessary."
I interpret this to mean it will exist by the next line.

+  NSString* unique_id = base::mac::ObjCCast<NSString>(
+      user_data_manager->GetValueForSerializationKey(kTabIDKey));
+  if (!unique_id || ![unique_id length]) {
+    unique_id = [[NSUUID UUID] UUIDString];
+    user_data_manager->AddSerializableData(unique_id, kTabIDKey);
+  }
+  tab_id_ = base::SysNSStringToUTF8(unique_id);
+}
+
+TabIDTabHelper::~TabIDTabHelper() = default;