Decompose //extensions/browser/BUILD.gn

extensions/browser/api/sockets_udp/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.
 
-import("//third_party/WebKit/Source/core/core.gni")
-
-blink_core_sources("imagebitmap") {
+source_set("sockets_udp") {
   sources = [
-    "ImageBitmapFactories.cpp",
-    "ImageBitmapFactories.h",
-    "ImageBitmapSource.cpp",
-    "ImageBitmapSource.h",
+    "sockets_udp_api.cc",
+    "sockets_udp_api.h",
+    "udp_socket_event_dispatcher.cc",
+    "udp_socket_event_dispatcher.h",
   ]
 
   configs += [
     # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
     "//build/config/compiler:no_size_t_to_int_warning",
   ]
+
+  deps = [
+    "//extensions/common/api",
+  ]
 }