predictors: Make speculative_prefetch_predictor work with PlzNavigate

chrome/browser/predictors/resource_prefetch_common.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_PREDICTORS_RESOURCE_PREFETCH_COMMON_H_
 #define CHROME_BROWSER_PREDICTORS_RESOURCE_PREFETCH_COMMON_H_
 
 #include <stddef.h>
 
 #include "base/time/time.h"
+#include "chrome/browser/sessions/session_tab_helper.h"
+#include "components/sessions/core/session_id.h"
 #include "url/gurl.h"
 
 class Profile;
 
 namespace content {
 class WebContents;
 }
 
 namespace predictors {
 
@@ skipping 15 matching lines @@
 enum class PrefetchOrigin { NAVIGATION, EXTERNAL };
 
 // Represents a single navigation for a render frame.
 struct NavigationID {
   NavigationID();
   explicit NavigationID(content::WebContents* web_contents);
   NavigationID(content::WebContents* web_contents,
                const GURL& main_frame_url,
                const base::TimeTicks& creation_time);
   NavigationID(const NavigationID& other);
+
   bool operator<(const NavigationID& rhs) const;
   bool operator==(const NavigationID& rhs) const;
 
-  bool IsSameRenderer(const NavigationID& other) const;
-
   // Returns true iff the render_process_id_, render_frame_id_ and
   // frame_url_ has been set correctly.
   bool is_valid() const;
 
-  int render_process_id;
-  int render_frame_id;
+  SessionID session_id;

[Benoit L, 2016/12/19 16:55:55]

Looking at the code of SessionID, merely constructing a SessionID increases the
value of the next one (in the constructor).

Can you store a SessionID::id_type instead?

It is an int32_t, and I don't think we risk any wraparound issue here, but
perhaps some code somewhere doesn't expect it to increase really fast. Keeping a
SessionID here would create a new one for each request, at least.

Also, it makes the construction  (and copying) of NavigationID subtly
not-threadsafe.

Finally, it matches the return type of

static SessionID::id_type IdForTab(const content::WebContents* tab);

   GURL main_frame_url;
 
   // NOTE: Even though we store the creation time here, it is not used during
   // comparison of two NavigationIDs because it cannot always be determined
   // correctly.
   base::TimeTicks creation_time;
 };
 
 // Represents the config for the resource prefetch prediction algorithm.
 struct ResourcePrefetchPredictorConfig {
@@ skipping 48 matching lines @@
   // Maximum number of prefetches that can be inflight for a single navigation.
   size_t max_prefetches_inflight_per_navigation;
   // Maximum number of prefetches that can be inflight for a host for a single
   // navigation.
   size_t max_prefetches_inflight_per_host_per_navigation;
 };
 
 }  // namespace predictors
 
 #endif  // CHROME_BROWSER_PREDICTORS_RESOURCE_PREFETCH_COMMON_H_