Introduce the ENABLE_BROWSER_CDMS macro.

media/base/browser_cdm.h

Index: media/base/browser_cdm.h
diff --git a/media/base/browser_cdm.h b/media/base/browser_cdm.h
index b6b6044c4d7504af258e000f3115da9f38018d27..f009779324dfeee43a27498ae4ba377be53dbbab 100644
--- a/media/base/browser_cdm.h
+++ b/media/base/browser_cdm.h
@@ -5,13 +5,14 @@
 #ifndef MEDIA_BASE_BROWSER_CDM_H_
 #define MEDIA_BASE_BROWSER_CDM_H_
 
+#include "media/base/media_export.h"
 #include "media/base/media_keys.h"
 #include "media/base/player_tracker.h"
 
 namespace media {
 
 // Interface for browser side CDMs.
-class BrowserCdm : public PlayerTracker {
+class MEDIA_EXPORT BrowserCdm : public PlayerTracker {
  public:
   // TODO(jrummell): Update this to actually derive from MediaKeys
   // (Use web_session_id rather than session_id).