Add an IPC to return the platform supported key-system names in Android.

media/base/android/media_drm_bridge.h

Index: media/base/android/media_drm_bridge.h
diff --git a/media/base/android/media_drm_bridge.h b/media/base/android/media_drm_bridge.h
index a7a28bd3b627e0e4bfa74f5e5f0c1cfa985ac835..8c33a334617dfcb67ad70c12ce6591dcce67f794 100644
--- a/media/base/android/media_drm_bridge.h
+++ b/media/base/android/media_drm_bridge.h
@@ -48,6 +48,10 @@ class MEDIA_EXPORT MediaDrmBridge : public BrowserCdm {
   // Checks whether |key_system| is supported.
   static bool IsKeySystemSupported(const std::string& key_system);
 
+  // Returns the list of the platform-supported key system names that
+  // are not handled by Chrome explicitly.
+  static std::vector<std::string> GetPlatformKeySystemNames();
+
   // Adds a new |key_system| with the associated |uuid|.
   // This is used for other platforms to have a chance to register their
   // own UUID mapping.