Add UserInputTracker, which keeps track of recent user input events.

chrome/browser/page_load_metrics/user_input_tracker.h

Index: chrome/browser/page_load_metrics/user_input_tracker.h
diff --git a/chrome/browser/page_load_metrics/user_input_tracker.h b/chrome/browser/page_load_metrics/user_input_tracker.h
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index 0000000000000000000000000000000000000000..cfb020e5778f358a6b0aff8271f1e439a636a0ca
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+++ b/chrome/browser/page_load_metrics/user_input_tracker.h
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+// Copyright 2016 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_PAGE_LOAD_METRICS_USER_INPUT_TRACKER_H_
+#define CHROME_BROWSER_PAGE_LOAD_METRICS_USER_INPUT_TRACKER_H_
+
+#include <set>
+
+#include "base/time/time.h"
+
+namespace blink {
+class WebInputEvent;
+}  // namespace blink
+
+namespace page_load_metrics {
+
+// UserInputTracker keeps track of user input events processed by web pages, and
+// allows clients to find and consume those input events. This allows us to
+// heuristically attribute user input events to navigations, in order to keep
+// track of which page loads and aborts were initiated by a user action.
+//
+// There are issues with the existing user gesture tracking in Blink and content
+// that make it unsuitable for our needs. For example, Blink considers events
+// such as navigations that occur within 1 second of a user action event to have
+// been initiated by a user action, based on the HTML spec
+// (https://html.spec.whatwg.org/multipage/interaction.html#triggered-by-user-activation).
+// This can be problematic in cases where a web page issues many navigations in
+// rapid succession, e.g. from a JavaScript tight loop, as all of the

[Charlie Harrison, 2016/12/02 02:58:44]

"e.g. JS code that dispatches new navigation requests in a tight loop can result
in dozens of programmatically generated navigations being user initiated." You
can cut some of the words here that are redundant, and the bit about 30ms is too
much detail imo.

[Bryan McQuade, 2016/12/02 20:43:01]

Done

+// navigations issued within a second of a user action will be attributed to a
+// user action by default. For JS code running in a tight loop that dispatches a
+// new navigation request every ~30ms, this can result in dozens of
+// programatically generated navigations being considered as user
+// initiated. UserInputTracker is used to associate at most one navigation with
+// a given input event that was generated before the navigation event.
+//
+// Note that UserInputTracker does not keep track of input events processed by
+// the browser, such as interactions with the Chrome browser UI (e.g. clicking
+// the 'reload' button).
+class UserInputTracker {
+ public:
+  static base::TimeTicks GetEventTime(const blink::WebInputEvent& event);
+
+  UserInputTracker();
+  ~UserInputTracker();
+
+  void OnInputEvent(const blink::WebInputEvent& event);
+
+  // Finds the time of the most recent user input event before the given time,
+  // or a null TimeTicks if there are no user input events before the given
+  // time.
+  base::TimeTicks FindMostRecentUserInputEventBefore(base::TimeTicks time);
+
+  // Consumes all user input events up to the specified time.
+  void ConsumeUserInputEventsUpTo(base::TimeTicks time);
+
+ private:
+  void RemoveInputEventsUpTo(base::TimeTicks cutoff);
+  void RemoveOldInputEvents();
+  static base::TimeTicks GetOldestAllowedEventTime();
+
+  std::set<base::TimeTicks> event_times_;

[Charlie Harrison, 2016/12/02 02:58:44]

Can this be a sorted vector instead?

[Bryan McQuade, 2016/12/02 20:43:01]

Yeah - we discussed this & I made the switch.

+
+  DISALLOW_COPY_AND_ASSIGN(UserInputTracker);
+};
+
+}  // namespace page_load_metrics
+
+#endif  // CHROME_BROWSER_PAGE_LOAD_METRICS_USER_INPUT_TRACKER_H_