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

ios/chrome/browser/ui/commands/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("commands") {
+  sources = [
+    "UIKit+ChromeExecuteCommand.h",
+    "UIKit+ChromeExecuteCommand.mm",
+    "clear_browsing_data_command.h",
+    "clear_browsing_data_command.mm",
+    "generic_chrome_command.h",
+    "generic_chrome_command.mm",
+    "ios_command_ids.h",
+    "open_url_command.h",
+    "open_url_command.mm",
+    "reading_list_add_command.h",
+    "reading_list_add_command.mm",
+    "set_up_for_testing_command.h",
+    "set_up_for_testing_command.mm",
+    "show_mail_composer_command.h",
+    "show_mail_composer_command.mm",
+    "show_signin_command.h",
+    "show_signin_command.mm",
+  ]
+  deps = [
+    "//base",
+    "//components/browsing_data/core",
+    "//components/signin/core/browser",
+    "//ios/web",
+    "//net",
+    "//url",
+  ]
+}
+
+source_set("unit_tests") {
+  testonly = true
+  sources = [
+    "set_up_for_testing_command_unittest.mm",
+  ]
+  deps = [
+    ":commands",
+    "//base",
+    "//testing/gtest",
+    "//url",
+  ]
+}