predictors: Introduce GlowplugPredictor.

chrome/browser/predictors/glowplug_predictor.h

+// Copyright 2017 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_PREDICTORS_GLOWPLUG_PREDICTOR_H_
+#define CHROME_BROWSER_PREDICTORS_GLOWPLUG_PREDICTOR_H_
+
+#include <memory>
+
+#include "base/memory/weak_ptr.h"
+#include "chrome/browser/predictors/resource_prefetch_common.h"
+#include "chrome/browser/predictors/resource_prefetch_predictor.h"
+#include "components/keyed_service/core/keyed_service.h"
+
+class Profile;
+
+namespace predictors {
+
+class ResourcePrefetchPredictor;
+
+// All methods must be called from the UI thread.

[alexilin, 2017/05/11 16:53:12]

Shouldn't we have here a detailed description of the Glowplug since it's an
entry point? 

[Benoit L, 2017/05/12 12:12:52]

Done.

+class GlowplugPredictor : public KeyedService,
+                          public base::SupportsWeakPtr<GlowplugPredictor> {
+ public:
+  GlowplugPredictor(const GlowplugPredictorConfig& config, Profile* profile);
+  ~GlowplugPredictor() override;
+
+  // Starts prefetching if it is enabled for |origin| and prefetching data
+  // exists for the |main_frame_url| either at the URL or at the host level.
+  void StartPrefetching(const GURL& main_frame_url, PrefetchOrigin origin);

[alexilin, 2017/05/11 16:53:12]

Do you want to keep this function name? I think now is the best moment to rename
it as you wanted.

[Benoit L, 2017/05/12 12:12:52]

Done.

+  // Stops prefetching that may be in progress corresponding to
+  // |main_frame_url|.
+  void StopPrefetching(const GURL& main_frame_url);
+
+  ResourcePrefetchPredictor* resource_prefetch_predictor() const;

[alexilin, 2017/05/11 16:53:12]

As I understand, it's temporary for clients who will use data collection
interface after refactoring, right?

Currently I see a problem that users of GlowplugPredictor could keep using raw
pointer after GlowplugPredictor destruction.

[Benoit L, 2017/05/12 12:12:52]

Yes, it's temporary. Added a comment.
Getting a raw pointer doesn't imply ownership. And the lifetime of it is tied to
the lifetime of GlowplugPredictor, so clients are fine.

[alexilin, 2017/05/12 14:26:45]

Clients could outlive GlowplugPredictor while keeping the pointer and
accidentally use it after GlowplugPredictor destruction. Though, it would mean
that a client uses GlowplugPredictor without explicitly declaring dependency on
it, that's bad.

[Benoit L, 2017/05/12 15:13:11]

Per offline discussion, no issues here, since the only client caching the
pointer declares the dependency.

+
+  // KeyedService methods override.
+  void Shutdown() override;
+
+ private:
+  std::unique_ptr<ResourcePrefetchPredictor> resource_prefetch_predictor_;
+
+  DISALLOW_COPY_AND_ASSIGN(GlowplugPredictor);
+};
+
+}  // namespace predictors
+
+#endif  // CHROME_BROWSER_PREDICTORS_GLOWPLUG_PREDICTOR_H_