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

ios/chrome/browser/signin/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("signin") {
   sources = [
     "about_signin_internals_factory.cc",
     "about_signin_internals_factory.h",
     "account_consistency_service_factory.h",
     "account_consistency_service_factory.mm",
@@ skipping 32 matching lines @@
     "signin_error_controller_factory.h",
     "signin_manager_factory.cc",
     "signin_manager_factory.h",
     "signin_manager_factory_observer.h",
     "signin_util.h",
     "signin_util.mm",
   ]
   deps = [
     "//components/browser_sync",
     "//components/sync",
+    "//ios/chrome/browser:browser_no_public_deps",
+    "//ios/chrome/browser/bookmarks:bookmarks_utils",
+    "//ios/chrome/browser/browser_state",
+    "//ios/chrome/browser/content_settings",
+    "//ios/chrome/browser/crash_report",
+    "//ios/chrome/browser/ui/commands",
     "//ios/web",
     "//url",
   ]
   public_deps = [
     "//base",
     "//components/content_settings/core/browser",
     "//components/keyed_service/core",
     "//components/keyed_service/ios",
     "//components/metrics",
     "//components/pref_registry",
@@ skipping 45 matching lines @@
     "//components/prefs",
     "//components/signin/core/browser",
     "//components/signin/core/browser:test_support",
     "//components/signin/core/common",
     "//components/signin/ios/browser",
     "//components/syncable_prefs",
     "//components/syncable_prefs:test_support",
     "//google_apis",
     "//ios/chrome/browser",
     "//ios/chrome/browser:test_support",
-    "//ios/chrome/test",
+    "//ios/chrome/test:test_support",
     "//ios/public/provider/chrome/browser",
     "//ios/public/provider/chrome/browser:test_support",
     "//ios/web:test_support",
     "//net:test_support",
     "//testing/gmock",
     "//testing/gtest",
     "//third_party/ocmock",
   ]
 }