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

ios/chrome/browser/prefs/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("prefs") {
+  sources = [
+    "browser_prefs.h",
+    "browser_prefs.mm",
+    "ios_chrome_pref_model_associator_client.cc",
+    "ios_chrome_pref_model_associator_client.h",
+    "ios_chrome_pref_service_factory.cc",
+    "ios_chrome_pref_service_factory.h",
+    "pref_observer_bridge.h",
+    "pref_observer_bridge.mm",
+  ]
+  deps = [
+    "//base",
+    "//components/autofill/core/browser",
+    "//components/browsing_data/core",
+    "//components/content_settings/core/browser",
+    "//components/dom_distiller/core",
+    "//components/flags_ui",
+    "//components/gcm_driver",
+    "//components/network_time",
+    "//components/ntp_snippets",
+    "//components/ntp_tiles",
+    "//components/omnibox/browser",
+    "//components/password_manager/core/browser",
+    "//components/pref_registry",
+    "//components/prefs",
+    "//components/proxy_config",
+    "//components/rappor",
+    "//components/search_engines",
+    "//components/signin/core/common",
+    "//components/ssl_config",
+    "//components/strings",
+    "//components/sync",
+    "//components/syncable_prefs",
+    "//components/translate/core/browser",
+    "//components/translate/core/common",
+    "//components/update_client",
+    "//components/variations/service",
+    "//components/web_resource",
+    "//ios/chrome/browser:browser_no_public_deps",
+    "//ios/chrome/browser/browser_state",
+    "//ios/chrome/browser/first_run",
+    "//ios/chrome/browser/geolocation",
+    "//ios/chrome/browser/memory",
+    "//ios/chrome/browser/metrics",
+    "//ios/chrome/browser/net",
+    "//ios/chrome/browser/signin",
+    "//ios/public/provider/chrome/browser",
+    "//ui/base",
+  ]
+}