Decompose //extensions/browser/BUILD.gn

extensions/browser/api/socket/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("socket") {
+  sources = [
+    "socket.cc",
+    "socket.h",
+    "socket_api.cc",
+    "socket_api.h",
+    "tcp_socket.cc",
+    "tcp_socket.h",
+    "tls_socket.cc",
+    "tls_socket.h",
+    "udp_socket.cc",
+    "udp_socket.h",
+  ]
+
+  if (is_chromeos) {
+    sources += [
+      "app_firewall_hole_manager.cc",
+      "app_firewall_hole_manager.h",
+    ]
+  }
+
+  configs += [
+    # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
+    "//build/config/compiler:no_size_t_to_int_warning",
+  ]
+
+  deps = [
+    "//content/public/browser",
+    "//content/public/common",
+    "//extensions/common/api",
+  ]
+}