Introduce the ENABLE_BROWSER_CDMS macro.

content/content_browser.gypi

Index: content/content_browser.gypi
diff --git a/content/content_browser.gypi b/content/content_browser.gypi
index 4758aeb97a816d37a443e0582d27944be871ab94..13d12a1866eb2404d0c21c754d2cb5ff1ba98f2d 100644
--- a/content/content_browser.gypi
+++ b/content/content_browser.gypi
@@ -781,8 +781,6 @@
       'browser/loader/upload_data_stream_builder.h',
       'browser/mach_broker_mac.h',
       'browser/mach_broker_mac.mm',
-      'browser/media/android/browser_cdm_manager.cc',
-      'browser/media/android/browser_cdm_manager.h',
       'browser/media/android/browser_demuxer_android.cc',
       'browser/media/android/browser_demuxer_android.h',
       'browser/media/android/browser_media_player_manager.cc',
@@ -791,8 +789,6 @@
       'browser/media/android/media_drm_credential_manager.h',
       'browser/media/android/media_resource_getter_impl.cc',
       'browser/media/android/media_resource_getter_impl.h',
-      'browser/media/android/media_web_contents_observer.cc',
-      'browser/media/android/media_web_contents_observer.h',
       'browser/media/capture/audio_mirroring_manager.cc',
       'browser/media/capture/audio_mirroring_manager.h',
       'browser/media/capture/content_video_capture_device_core.cc',
@@ -1764,5 +1760,14 @@
         'browser/geolocation/wifi_data_provider_linux.cc',
       ],
     }],
+    ['enable_browser_cdms==1', {
+      'sources': [
+        'browser/media/cdm/browser_cdm_manager.cc',
+        'browser/media/cdm/browser_cdm_manager.h',
+        # This works on Android because enable_browser_cdms==1 on Android.
+        'browser/media/media_web_contents_observer.cc',
+        'browser/media/media_web_contents_observer.h',
+      ],
+    }],
   ],
 }