Re-add resource speculative prefetching code

chrome/browser/predictors/resource_prefetch_common.h

Index: chrome/browser/predictors/resource_prefetch_common.h
diff --git a/chrome/browser/predictors/resource_prefetch_common.h b/chrome/browser/predictors/resource_prefetch_common.h
new file mode 100644
index 0000000000000000000000000000000000000000..f94a50dbe08918757dcb6889141c275a15076106
--- /dev/null
+++ b/chrome/browser/predictors/resource_prefetch_common.h
@@ -0,0 +1,116 @@
+// 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 "base/time/time.h"
+#include "url/gurl.h"
+
+class Profile;
+
+namespace content {
+class WebContents;
+}
+
+namespace predictors {
+
+struct ResourcePrefetchPredictorConfig;
+
+// Returns true if prefetching is enabled. And will initilize the |config|
+// fields to the appropritate values.
+bool IsSpeculativeResourcePrefetchingEnabled(
+    Profile* profile,
+    ResourcePrefetchPredictorConfig* config);
+
+// Represents the type of key based on which prefetch data is stored.
+enum PrefetchKeyType {
+  PREFETCH_KEY_TYPE_HOST,
+  PREFETCH_KEY_TYPE_URL
+};
+
+// Represents a single navigation for a render frame.
+struct NavigationID {
+  // TODO(shishir): Maybe take process_id, frame_id and url as input in
+  // constructor.
+  NavigationID();
+  NavigationID(const NavigationID& other);
+  explicit NavigationID(content::WebContents* web_contents);
+  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;
+  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. It is
+// useful for running experiments.
+struct ResourcePrefetchPredictorConfig {
+  // Initializes the config with default values.
+  ResourcePrefetchPredictorConfig();
+  ~ResourcePrefetchPredictorConfig();
+
+  // The mode the prefetcher is running in. Forms a bit map.
+  enum Mode {
+    URL_LEARNING    = 1 << 0,
+    HOST_LEARNING   = 1 << 1,
+    URL_PREFETCHING = 1 << 2,  // Should also turn on URL_LEARNING.
+    HOST_PRFETCHING = 1 << 3   // Should also turn on HOST_LEARNING.
+  };
+  int mode;
+
+  // Helpers to deal with mode.
+  bool IsLearningEnabled() const;
+  bool IsPrefetchingEnabled() const;
+  bool IsURLLearningEnabled() const;
+  bool IsHostLearningEnabled() const;
+  bool IsURLPrefetchingEnabled() const;
+  bool IsHostPrefetchingEnabled() const;
+
+  // If a navigation hasn't seen a load complete event in this much time, it
+  // is considered abandoned.
+  size_t max_navigation_lifetime_seconds;
+
+  // Size of LRU caches for the URL and host data.
+  size_t max_urls_to_track;
+  size_t max_hosts_to_track;
+
+  // The number of times we should have seen a visit to this URL in history
+  // to start tracking it. This is to ensure we don't bother with oneoff
+  // entries. For hosts we track each one.
+  size_t min_url_visit_count;
+
+  // The maximum number of resources to store per entry.
+  size_t max_resources_per_entry;
+  // The number of consecutive misses after we stop tracking a resource URL.
+  size_t max_consecutive_misses;
+
+  // The minimum confidence (accuracy of hits) required for a resource to be
+  // prefetched.
+  float min_resource_confidence_to_trigger_prefetch;
+  // The minimum number of times we must have a URL on record to prefetch it.
+  size_t min_resource_hits_to_trigger_prefetch;
+
+  // 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_