Decompose //extensions/browser/BUILD.gn

extensions/browser/api/display_source/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("//build/config/features.gni")
+
+source_set("display_source") {
+  sources = [
+    "display_source_api.cc",
+    "display_source_api.h",
+    "display_source_connection_delegate.cc",
+    "display_source_connection_delegate.h",
+    "display_source_connection_delegate_factory.cc",
+    "display_source_connection_delegate_factory.h",
+    "display_source_event_router.cc",
+    "display_source_event_router.h",
+    "display_source_event_router_factory.cc",
+    "display_source_event_router_factory.h",
+  ]
+
+  if (!is_chromeos) {
+    if (proprietary_codecs && enable_wifi_display) {
+      sources += [
+        "wifi_display/wifi_display_media_service_impl.cc",
+        "wifi_display/wifi_display_media_service_impl.h",
+        "wifi_display/wifi_display_session_service_impl.cc",
+        "wifi_display/wifi_display_session_service_impl.h",
+      ]
+    }
+  }
+
+  deps = [
+    "//extensions/common/api",
+  ]
+}