Create headerHeightForTab in TabHeadersDelegate.

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 = [
     "tab.h",
     "tab_delegate.h",
     "tab_dialog_delegate.h",
+    "tab_headers_delegate.h",
     "tab_model.h",
     "tab_model_list.h",
     "tab_model_observer.h",
     "tab_model_order_controller.h",
     "tab_model_synced_window_delegate.h",
     "tab_model_synced_window_delegate_getter.h",
     "tab_private.h",
     "tab_snapshotting_delegate.h",
   ]
   deps = [
@@ skipping 154 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" ]
 }