Decompose //extensions/browser/BUILD.gn

extensions/browser/app_window/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("app_window") {
+  sources = [
+    "app_delegate.h",
+    "app_web_contents_helper.cc",
+    "app_web_contents_helper.h",
+    "app_window.cc",
+    "app_window.h",
+    "app_window_client.cc",
+    "app_window_client.h",
+    "app_window_contents.cc",
+    "app_window_contents.h",
+    "app_window_geometry_cache.cc",
+    "app_window_geometry_cache.h",
+    "app_window_registry.cc",
+    "app_window_registry.h",
+    "native_app_window.h",
+    "size_constraints.cc",
+    "size_constraints.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/common",
+    "//extensions/strings",
+  ]
+}