PageLoadMetrics renderer and browser implementation.

components/page_load_metrics/common/page_load_timing.h

+// Copyright 2015 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 COMPONENTS_PAGE_LOAD_METRICS_COMMON_PAGE_LOAD_TIMING_H_
+#define COMPONENTS_PAGE_LOAD_METRICS_COMMON_PAGE_LOAD_TIMING_H_
+
+#include "base/time/time.h"
+
+namespace blink {
+class WebPerformance;
+}
+
+namespace page_load_metrics {
+
+// PageLoadTiming contains timing metrics associated with a page load. Many of
+// the metrics here are based on the Navigation Timing spec:
+// http://www.w3.org/TR/navigation-timing/.
+struct PageLoadTiming {
+ public:
+  PageLoadTiming();
+  PageLoadTiming(blink::WebPerformance&);

[Bryan McQuade, 2015/09/02 18:26:46]

can you make the function parameter const?

[Charlie Harrison, 2015/09/03 14:00:52]

Done.

+  ~PageLoadTiming();
+
+  bool operator==(const PageLoadTiming& other) const;

[Bryan McQuade, 2015/09/02 18:26:46]

I think randy had suggested trying to use the default implementation here (c++11
feature) - can you try changing this to:

bool operator==(const PageLoadTiming& other) const = default;

and removing the implementation in the cc file, and seeing if that works as
intended? I've never used 'default' for equality, so I'm not sure if it's
actually supported (or exactly how it works) but I think it's worth trying and
learning more about.

[Charlie Harrison, 2015/09/03 14:00:52]

According to this: http://en.cppreference.com/w/cpp/language/member_functions,
equality is not a special member function and cannot be defaulted.

+
+  // Returns true if |parent| is equal to |this| besides for uninitialized
+  // fields in |parent|
+  bool IsChild(const PageLoadTiming& parent) const;

[Bryan McQuade, 2015/09/02 18:26:46]

Though these methods logically make sense as members, the recommendation in the
style guide is that structs should only contain data, and not functions. See
http://google-styleguide.googlecode.com/svn/trunk/cppguide.html#Structs_vs._C....

Normally I might suggest that we should just change this to a class, but given
that it is sent over IPC, and in general IPC wants to deal with just moving data
around, I think there is value in keeping it a struct.

If the logic in these methods is only needed in the web contents observer, it
may be worth adding them as helper methods that take a 'const PageLoadTiming&'
as an argument, in an anonymous namespace in the cc file.

I think it's worth asking Randy or someone else about this before making a
change though, since it's not 100% clear cut and I'd like to get a second
opinion.

[Charlie Harrison, 2015/09/03 14:00:52]

Randy said it's reasonable to move them, but he isn't sure of the ins and outs
of IPC code. I'll make the change.

+
+  bool IsComplete() const;
+  bool IsEmpty() const;
+  // Checks guaranteed ordering for performance events.
+  // Assumes IsComplete()
+  bool IsOrdered() const;
+
+  // Time that the navigation for the associated page was initiated.
+  base::Time navigation_start;
+
+  // Time that the first byte of the response is received.
+  base::TimeDelta response_start;
+
+  // Time immediately before the DOMContentLoaded event is fired.
+  base::TimeDelta dom_content_loaded_event_start;
+
+  // Time immediately before the load event is fired.
+  base::TimeDelta load_event_start;
+
+  // Time when the first layout is completed.
+  base::TimeDelta first_layout;
+
+  // If you add additional members, also be sure to update operator== and
+  // page_load_metrics_messages.h
+ private:
+  base::TimeDelta ClampDelta(double event_ms, double start_ms) const;
+};
+
+}  // namespace page_load_metrics
+
+#endif  // COMPONENTS_PAGE_LOAD_METRICS_COMMON_PAGE_LOAD_TIMING_H_