Revert CL 117933003. Re-add resource speculative prefetching code.

chrome/browser/net/resource_prefetch_predictor_observer.h

+// Copyright 2014 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 CHROME_BROWSER_NET_RESOURCE_PREFETCH_PREDICTOR_OBSERVER_H_
+#define CHROME_BROWSER_NET_RESOURCE_PREFETCH_PREDICTOR_OBSERVER_H_
+
+#include "base/basictypes.h"
+#include "base/memory/weak_ptr.h"
+#include "chrome/browser/predictors/resource_prefetch_predictor.h"
+#include "content/public/common/resource_type.h"
+
+namespace net {
+class URLRequest;
+}
+
+class GURL;
+
+namespace chrome_browser_net {
+
+// Observes resource requests in the ResourceDispatcherHostDelegate and notifies
+// the ResourcePrefetchPredictor about the ones it is interested in.
+//  - Has an instance per profile, and is owned by the corresponding
+//    ProfileIOData.
+//  - Needs to be constructed on UI thread. Rest of the functions can only be
+//    called on the IO thread. Can be destroyed on UI or IO thread.
+class ResourcePrefetchPredictorObserver {
+ public:
+  explicit ResourcePrefetchPredictorObserver(
+      predictors::ResourcePrefetchPredictor* predictor);
+  ~ResourcePrefetchPredictorObserver();
+
+  // Parts of the ResourceDispatcherHostDelegate that we want to observe.
+  void OnRequestStarted(net::URLRequest* request,
+                        content::ResourceType resource_type,
+                        int child_id,
+                        int frame_id);
+  void OnRequestRedirected(const GURL& redirect_url, net::URLRequest* request);
+  void OnResponseStarted(net::URLRequest* request);
+
+ private:
+  // Owned by profile.
+  base::WeakPtr<predictors::ResourcePrefetchPredictor> predictor_;
+
+  DISALLOW_COPY_AND_ASSIGN(ResourcePrefetchPredictorObserver);
+};
+
+}  // namespace chrome_browser_net
+
+#endif  // CHROME_BROWSER_NET_RESOURCE_PREFETCH_PREDICTOR_OBSERVER_H_