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 87079c1f60485bae679153fff5ba3319a4ebc816..f29b0b5367ce83deb28a625a3161d3f031a1d59b 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 be stored in 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.