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..7bf5b81e85e3145581e961603b043b1cb8c0482d 100644
--- a/content/public/browser/media_device_id.h
+++ b/content/public/browser/media_device_id.h
@@ -13,6 +13,7 @@
 #include <string>
 
 #include "content/common/content_export.h"
+#include "content/public/browser/resource_context.h"
 #include "url/gurl.h"
 
 namespace content {
@@ -20,12 +21,14 @@ namespace content {
 // 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);