Allow retrieval of media device ID salt even after ResourceContext has gone away.

content/browser/resource_context_impl.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/resource_context_impl.h"
 
 #include "base/logging.h"
 #include "content/browser/fileapi/chrome_blob_storage_context.h"
 #include "content/browser/host_zoom_map_impl.h"
 #include "content/browser/loader/resource_dispatcher_host_impl.h"
@@ skipping 19 matching lines @@
 
 class NonOwningZoomData : public base::SupportsUserData::Data {
  public:
   explicit NonOwningZoomData(HostZoomMap* hzm) : host_zoom_map_(hzm) {}
   HostZoomMap* host_zoom_map() { return host_zoom_map_; }
 
  private:
   HostZoomMap* host_zoom_map_;
 };
 
+// Used by the default implementation of GetMediaDeviceIDSalt, below.
+std::string ReturnEmptySalt() {
+  return std::string();
+}
+
 }  // namespace
 
 
 ResourceContext::ResourceContext() {
   if (ResourceDispatcherHostImpl::Get())
     ResourceDispatcherHostImpl::Get()->AddResourceContext(this);
 }
 
 ResourceContext::~ResourceContext() {
   ResourceDispatcherHostImpl* rdhi = ResourceDispatcherHostImpl::Get();
   if (rdhi) {
     rdhi->CancelRequestsForContext(this);
     rdhi->RemoveResourceContext(this);
   }
 
   // In some tests this object is destructed on UI thread.
   DetachUserDataThread();
 }
 
-std::string ResourceContext::GetMediaDeviceIDSalt() {
-  return std::string();
+ResourceContext::SaltCallback ResourceContext::GetMediaDeviceIDSalt() {
+  return base::Bind(&ReturnEmptySalt);
 }
 
 scoped_ptr<net::ClientCertStore> ResourceContext::CreateClientCertStore() {
   return scoped_ptr<net::ClientCertStore>();
 }
 
 void ResourceContext::CreateKeygenHandler(
     uint32 key_size_in_bits,
     const std::string& challenge_string,
     const GURL& url,
@@ skipping 51 matching lines @@
   // store a non-owning pointer here.
   resource_context->SetUserData(
       kHostZoomMapKeyName,
       new NonOwningZoomData(
           HostZoomMap::GetForBrowserContext(browser_context)));
 
   resource_context->DetachUserDataThread();
 }
 
 }  // namespace content