Add Explicit Argument Guidance for time.h

base/time/time.h

 // Copyright (c) 2012 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.
 
 // Time represents an absolute point in coordinated universal time (UTC),
 // internally represented as microseconds (s/1,000,000) since the Windows epoch
 // (1601-01-01 00:00:00 UTC). System-dependent clock interface routines are
 // defined in time_PLATFORM.cc. Note that values for Time may skew and jump
 // around as the operating system makes adjustments to synchronize (e.g., with
 // NTP servers). Thus, client code that uses the Time class must account for
 // this.
 //
 // TimeDelta represents a duration of time, internally represented in
 // microseconds.
 //
 // TimeTicks and ThreadTicks represent an abstract time that is most of the time
 // incrementing, for use in measuring time durations. Internally, they are
 // represented in microseconds. They can not be converted to a human-readable
 // time, but are guaranteed not to decrease (unlike the Time class). Note that
 // TimeTicks may "stand still" (e.g., if the computer is suspended), and
 // ThreadTicks will "stand still" whenever the thread has been de-scheduled by
 // the operating system.
 //
 // All time classes are copyable, assignable, and occupy 64-bits per
 // instance. Thus, they can be efficiently passed by-value (as opposed to
 // by-reference).
 //
+// Prefer passing these classes by value:

[danakj, 2016/09/30 20:18:56]

can you combine these two comments then cuz saying it twice is weird. like..

As time classes occupy 64-bits per instance, prefer passing these classes by
value:

or something?

[robliao, 2016/09/30 20:26:29]

Done!

// All time classes are copyable, assignable, and occupy 64-bits per instance.
// As a result, prefer passing them by value:
//   void MyFunction(TimeDelta arg);
// If circumstances require, you may also pass by const reference:
//   void MyFunction(const TimeDelta& arg);  // Not preferred.

+//   void MyFunction(TimeDelta arg);
+// If circumstances require, you may also pass by const reference:
+//   void MyFunction(const TimeDelta& arg);  // Not preferred.
+//
 // Definitions of operator<< are provided to make these types work with
 // DCHECK_EQ() and other log macros. For human-readable formatting, see
 // "base/i18n/time_formatting.h".
 //
 // So many choices!  Which time class should you use?  Examples:
 //
 //   Time:        Interpreting the wall-clock time provided by a remote
 //                system. Detecting whether cached resources have
 //                expired. Providing the user with a display of the current date
 //                and time. Determining the amount of time between events across
@@ skipping 795 matching lines @@
   static void WaitUntilInitializedWin();
 #endif
 };
 
 // For logging use only.
 BASE_EXPORT std::ostream& operator<<(std::ostream& os, ThreadTicks time_ticks);
 
 }  // namespace base
 
 #endif  // BASE_TIME_TIME_H_