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

content/public/browser/media_device_id.h

Index: content/public/browser/media_device_id.h
diff --git a/content/public/browser/media_device_id.h b/content/public/browser/media_device_id.h
index 5c7358c367f9e195348f4d7a497d9ee294c48f5c..50a3e0c41d9e311317a0f387f54e5894b237af8d 100644
--- a/content/public/browser/media_device_id.h
+++ b/content/public/browser/media_device_id.h
@@ -17,15 +17,19 @@
 
 namespace content {
 
+class ResourceContext;
+
 // Generates a one-way hash of a device's unique ID usable by one
 // particular security origin.
 CONTENT_EXPORT std::string GetHMACForMediaDeviceID(
+    ResourceContext* rc,
     const GURL& security_origin,
     const std::string& raw_unique_id);
 
 // Convenience method to check if |device_guid| is an HMAC of
 // |raw_device_id| for |security_origin|.
 CONTENT_EXPORT bool DoesMediaDeviceIDMatchHMAC(
+    ResourceContext* rc,
     const GURL& security_origin,
     const std::string& device_guid,
     const std::string& raw_unique_id);