Decompose //extensions/browser/BUILD.gn

extensions/browser/guest_view/app_view/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.
 
-static_library("common") {
+source_set("app_view") {
   sources = [
-    "subresource_filter_message_generator.cc",
-    "subresource_filter_message_generator.h",
-    "subresource_filter_messages.h",
+    "app_view_constants.cc",
+    "app_view_constants.h",
+    "app_view_guest.cc",
+    "app_view_guest.h",
+    "app_view_guest_delegate.cc",
+    "app_view_guest_delegate.h",
   ]
+
   deps = [
-    "//components/subresource_filter/core/common",
     "//content/public/common",
-    "//ipc",
   ]
 }