Add missing header files to GN files (3 of N)

ios/chrome/browser/tabs/BUILD.gn

 # Copyright 2016 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.
 
 source_set("tabs") {
   sources = [
     "legacy_tab_helper.h",
     "tab.h",
     "tab_delegate.h",
     "tab_dialog_delegate.h",
@@ skipping 12 matching lines @@
     "//components/sync_sessions",
     "//ios/net",
     "//ios/web",
     "//ui/base",
   ]
   libs = [ "UIKit.framework" ]
 }
 
 source_set("tabs_internal") {
   sources = [
+    "tab.h",
     "tab.mm",
     "tab_model.mm",
     "tab_model_synced_window_delegate.mm",
     "tab_model_synced_window_delegate_getter.mm",
   ]
   deps = [
     ":tabs",
     ":tabs_internal_arc",
     "//base",
     "//components/content_settings/core/browser",
@@ skipping 166 matching lines @@
     ":tabs",
     ":tabs_internal",
     "//base",
     "//ios/chrome/browser/browser_state:test_support",
     "//ios/chrome/browser/sessions:test_support",
     "//ios/web:test_support",
     "//testing/gtest",
   ]
   configs += [ "//build/config/compiler:enable_arc" ]
 }