Split //ios/chrome/browser in multiple targets.

ios/chrome/browser/ui/keyboard/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.
 
-if (is_android) {
-  import("//build/config/android/rules.gni")
-}
-
-static_library("request_header") {
+source_set("keyboard") {
   sources = [
-    "offline_page_header.cc",
-    "offline_page_header.h",
+    "UIKeyCommand+Chrome.h",
+    "UIKeyCommand+Chrome.mm",
+    "hardware_keyboard_watcher.h",
+    "hardware_keyboard_watcher.mm",
   ]
-
   deps = [
     "//base",
+    "//ios/chrome/browser/ui/commands",
   ]
 }
 
 source_set("unit_tests") {
   testonly = true
   sources = [
-    "offline_page_header_unittest.cc",
+    "UIKeyCommand+ChromeTest.mm",
+    "hardware_keyboard_watcher_unittest.mm",
   ]
-
   deps = [
-    ":request_header",
+    ":keyboard",
     "//base",
     "//base/test:test_support",
+    "//ios/chrome/browser/ui/commands",
     "//testing/gtest",
+    "//third_party/ocmock",
   ]
 }