Refactor media out of WebContentsImpl to MediaWebContentsObserver.

content/browser/BUILD.gn

 # Copyright 2014 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")
 import("//build/config/ui.gni")
 import("//content/browser/browser.gni")
 import("//media/media_options.gni")
 
 source_set("browser") {
@@ skipping 499 matching lines @@
   }
 
   if (is_linux && use_dbus) {
     deps += [ "//dbus" ]
   }
 
   if (enable_browser_cdms) {
     sources += [
       "media/cdm/browser_cdm_manager.cc",
       "media/cdm/browser_cdm_manager.h",
-      "media/media_web_contents_observer.cc",
-      "media/media_web_contents_observer.h",
     ]
   }
 
   if (is_linux) {
     deps += [ "//third_party/boringssl" ]
   }
 
   if (enable_mojo_media != "none") {
     configs += [ "//media/mojo/services:enable_mojo_media_config" ]
   }
@@ skipping 14 matching lines @@
 
   if (enable_webvr && is_android) {
     sources += [
       "vr/android/cardboard/cardboard_vr_device.cc",
       "vr/android/cardboard/cardboard_vr_device.h",
       "vr/android/cardboard/cardboard_vr_device_provider.cc",
       "vr/android/cardboard/cardboard_vr_device_provider.h",
     ]
   }
 }