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
new file mode 100644
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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 <vector>
+
+#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. JS code that dispatches new navigation requests in a
+// tight loop can result in dozens of programmatically generated navigations
+// being user initiated.
+//
+// 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 const size_t kMaxEntries;

[Charlie Harrison, 2016/12/05 19:17:46]

s/kMaxEntries/kMaxTrackedEvents or something similar? kMaxEntries is very vague,
considering that from the public interface, UserInputTracker is not a container.

[Bryan McQuade, 2016/12/06 01:52:25]

Sure, renamed. This is only public for tests.

+
+  static base::TimeTicks GetEventTime(const blink::WebInputEvent& event);
+
+  // Given a time, round to the nearest rate-limited offset. UserInputTracker
+  // rate limits events, such that at most one event will be recorded per every
+  // 20ms. RoundToRateLimitedOffset round a TimeTicks down to its nearest whole
+  // 20ms.
+  static base::TimeTicks RoundToRateLimitedOffset(base::TimeTicks time);
+
+  UserInputTracker();
+  ~UserInputTracker();
+
+  void OnInputEvent(const blink::WebInputEvent& event);
+
+  // Attempts to find the most recent user input event before the given time,
+  // and, if that input event exists, consumes all events up to that
+  // event. Returns whether an input event before the given time was found and
+  // consumed.
+  bool FindAndConsumeInputEventsBefore(base::TimeTicks time);
+
+  // 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. Consumers of this class should use
+  // FindAndConsumeInputEventsBefore. This method is public only for testing.
+  base::TimeTicks FindMostRecentUserInputEventBefore(base::TimeTicks time);
+
+ private:
+  void RemoveInputEventsUpTo(base::TimeTicks cutoff);
+  void RemoveOldInputEvents();

[Charlie Harrison, 2016/12/05 19:17:46]

This one might need some documentation. What is "Old"?

[Bryan McQuade, 2016/12/06 01:52:25]

Done. It's somewhat of an implementation detail, but added a comment.

+  static base::TimeTicks GetOldestAllowedEventTime();
+
+  std::vector<base::TimeTicks> event_times_;

[Charlie Harrison, 2016/12/05 19:17:46]

Please document that this vector should always be sorted.

[Bryan McQuade, 2016/12/06 01:52:25]

Renamed to sorted_event_times_

+  base::TimeTicks most_recent_consumed_time_;
+
+  DISALLOW_COPY_AND_ASSIGN(UserInputTracker);
+};
+
+}  // namespace page_load_metrics
+
+#endif  // CHROME_BROWSER_PAGE_LOAD_METRICS_USER_INPUT_TRACKER_H_