Move detached files from web/ to (core/modules)/exported.

third_party/WebKit/Source/modules/exported/BUILD.gn

 # Copyright 2017 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/modules/modules.gni")
 
 blink_modules_sources("exported") {
   sources = [
     "WebCryptoNormalize.cpp",
     "WebDOMFileSystem.cpp",
     "WebDOMMediaStreamTrack.cpp",
     "WebDatabase.cpp",
+    "WebMediaDeviceChangeObserver.cpp",
+    "WebMediaStreamRegistry.cpp",
     "WebSpeechGrammar.cpp",
     "WebSpeechRecognitionHandle.cpp",
     "WebSpeechRecognitionResult.cpp",
   ]
 
   defines = [ "BLINK_MODULES_IMPLEMENTATION=1" ]
 }