ResourceScheduler should use renderer notifications instead of MRUCache to track renderers.

content/browser/loader/resource_scheduler_view_observer.h

+// Copyright (c) 2013 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.
+
+#ifndef CONTENT_BROWSER_LOADER_RESOURCE_SCHEDULER_VIEW_OBSERVER_H_
+#define CONTENT_BROWSER_LOADER_RESOURCE_SCHEDULER_VIEW_OBSERVER_H_
+
+#include "content/public/browser/notification_observer.h"
+#include "content/public/browser/notification_registrar.h"
+
+namespace content {
+
+// The ResourceScheduler needs to know when renderers are created and destroyed.
+// That happens on the UI thread, but the ResourceScheduler lives on the IO
+// thread. ResourceSchedulerViewObserver listens for renderer notifications on
+// the UI thread, then bounces them over to the IO thread so the
+// ResourceScheduler can be notified.
+class CONTENT_EXPORT ResourceSchedulerViewObserver

[darin (slow to review), 2013/03/13 00:12:27]

Another name for this might be RenderViewHostTracker.  It could be interesting
to the ResourceDispatcherHostImpl to be informed when RenderViewHosts get
destroyed.  It could ensure that all of the associated network requests get
terminated, for example.

So, you could end up layering this so that RenderViewHostTracker calls
ResourceDispatcherHostImpl methods, which calls ResourceScheduler methods.

Maybe that is overkill without good use cases, but it occurs to me that this
class doesn't really need to be specific to ResourceScheduler, so maybe its name
should be more generic.

+    : public NotificationObserver {
+ public:
+  ResourceSchedulerViewObserver();
+  virtual ~ResourceSchedulerViewObserver();
+
+ private:
+  // NotificationObserver interface:
+  virtual void Observe(int type,
+                       const NotificationSource& source,
+                       const NotificationDetails& details) OVERRIDE;
+
+  content::NotificationRegistrar registrar_;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_LOADER_RESOURCE_SCHEDULER_VIEW_OBSERVER_H_