Add Explicit Argument Guidance for time.h

base/time/time.h

Index: base/time/time.h
diff --git a/base/time/time.h b/base/time/time.h
index 648445f35a2394ec7bea7a5506a2dbd68ce12a67..fd09effc85dfd61015901b202e33a84120d90d5f 100644
--- a/base/time/time.h
+++ b/base/time/time.h
@@ -25,6 +25,11 @@
 // instance. Thus, they can be efficiently passed by-value (as opposed to

[danakj, 2016/09/30 19:57:47]

This is already said here though?

[robliao, 2016/09/30 20:03:06]

Agreed this discusses it, but in a non-opinionated way. This discussion below
makes an opinion on the best-practice. 

This came up in a code review earlier
(https://codereview.chromium.org/2383193002/). For StringPieces, we can simply
point to that comment. It's a little less clear with respect to time.h

 // by-reference).
 //
+// Prefer passing these classes by value:
+//   void MyFunction(TimeDelta arg);
+// If circumstances require, you may also pass by const reference:
+//   void MyFunction(const TimeDelta& arg);  // not preferred

[danakj, 2016/09/30 19:57:47]

nit:  // Not preferred.

[robliao, 2016/09/30 20:03:06]

Done.

+//
 // 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".