Implement a salt for MediaSource IDs that can be cleared by a user.

content/public/browser/content_browser_client.h

Index: content/public/browser/content_browser_client.h
diff --git a/content/public/browser/content_browser_client.h b/content/public/browser/content_browser_client.h
index dc7f9dd057c29299d8e8a4a4cd2ce5330f2fe460..3c746f4591cc2d61601ac9d4aeb65bdd5b15e72b 100644
--- a/content/public/browser/content_browser_client.h
+++ b/content/public/browser/content_browser_client.h
@@ -524,6 +524,11 @@ class CONTENT_EXPORT ContentBrowserClient {
   // else we should do with the file.
   virtual std::string GetDefaultDownloadName();
 
+  // Returns a random salt string that is used for creating MediaSourceIds.
+  // The salt should depend on the current user profile and should be reset if
+  // cookies are cleared. This is called on the IO thread.
+  virtual std::string GetMediaDeviceIDSalt(ResourceContext* rc);
+
   // Notification that a pepper plugin has just been spawned. This allows the
   // embedder to add filters onto the host to implement interfaces.
   // This is called on the IO thread.