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

ios/chrome/browser/first_run/BUILD.gn

Index: ios/chrome/browser/first_run/BUILD.gn
diff --git a/ios/chrome/browser/first_run/BUILD.gn b/ios/chrome/browser/first_run/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..59c221c1804e62f751d2bac03a1c75f2f5650386
--- /dev/null
+++ b/ios/chrome/browser/first_run/BUILD.gn
@@ -0,0 +1,18 @@
+# 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("first_run") {
+  sources = [
+    "first_run.h",
+    "first_run.mm",
+    "first_run_configuration.h",
+    "first_run_configuration.mm",
+    "first_run_metrics.h",
+  ]
+  deps = [
+    "//base",
+    "//components/pref_registry",
+    "//ios/chrome/browser:browser_no_public_deps",
+  ]
+}