Introduce the ENABLE_BROWSER_CDMS macro.

content/content_renderer.gypi

Index: content/content_renderer.gypi
diff --git a/content/content_renderer.gypi b/content/content_renderer.gypi
index fb316803439777b44ff547b2d18392a3810f9413..dd10f21be7460b8f4eb53a11251ea995a9e0ed9d 100644
--- a/content/content_renderer.gypi
+++ b/content/content_renderer.gypi
@@ -255,10 +255,6 @@
       'renderer/media/crypto/ppapi_decryptor.h',
       'renderer/media/crypto/proxy_decryptor.cc',
       'renderer/media/crypto/proxy_decryptor.h',
-      'renderer/media/crypto/proxy_media_keys.cc',
-      'renderer/media/crypto/proxy_media_keys.h',
-      'renderer/media/crypto/renderer_cdm_manager.cc',
-      'renderer/media/crypto/renderer_cdm_manager.h',
       'renderer/media/media_stream_audio_level_calculator.cc',
       'renderer/media/media_stream_audio_level_calculator.h',
       'renderer/media/media_stream_audio_renderer.cc',
@@ -828,6 +824,14 @@
         'renderer/media/crypto/ppapi_decryptor.h',
       ],
     }],
+    ['enable_browser_cdms==1', {
+      'sources': [
+        'renderer/media/crypto/proxy_media_keys.cc',
+        'renderer/media/crypto/proxy_media_keys.h',
+        'renderer/media/crypto/renderer_cdm_manager.cc',
+        'renderer/media/crypto/renderer_cdm_manager.h',
+      ],
+    }],
   ],
   'target_conditions': [
     ['OS=="android"', {