Minor tweaks to API documentation and code comments.

mojo/public/c/system/types.h

 // Copyright 2014 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.
 
 // This file contains types and constants/macros common to different Mojo system
 // APIs.
 //
 // Note: This header should be compilable as C.
 
 #ifndef MOJO_PUBLIC_C_SYSTEM_TYPES_H_
 #define MOJO_PUBLIC_C_SYSTEM_TYPES_H_
 
 #include <stdint.h>
 
 #include "mojo/public/c/system/macros.h"
 
 // TODO(vtl): Notes: Use of undefined flags will lead to undefined behavior
 // (typically they'll be ignored), not necessarily an error.
 
-// |MojoTimeTicks|: Used to specify time ticks. Value is in microseconds.
+// |MojoTimeTicks|: The amount of time, in units of microseconds, that has

[viettrungluu, 2015/01/30 22:34:17]

How about, simply: "A time delta, in microseconds, the meaning of which is
source-dependent."

[ggowan, 2015/01/30 23:17:12]

I think that somebody who is coming here to look at this definition would
probably also appreciate a reference to the MojoGetTimeTicksNow() function,
which, practically speaking, is the only place values of this type are likely to
come from.

However, I'll just put the text you've asked for since it's definitely an
improvement over what's there now. If you agree a reference to the function is
appropriate, I'll be happy to add it, perhaps in a follow-up CL.

+// passed since some undefined point in the past. The values are only meaningful
+// relative to other values obtained from the same device without an intervening
+// system restart. Such values are guaranteed to be weakly
+// monotonically-increasing with the passage of real time, meaning they will not
+// always advance, but they will never go backwards (unlike time values with a
+// well-defined epoch).  Although the units are microseconds, the values should
+// not be assumed to be at that level of precision. The actual precision varies
+// depending on hardware and platform, and is typically in the range of ~1-15
+// ms.
 
 typedef int64_t MojoTimeTicks;
 
 // |MojoHandle|: Handles to Mojo objects.
 //   |MOJO_HANDLE_INVALID| - A value that is never a valid handle.
 
 typedef uint32_t MojoHandle;
 
 #ifdef __cplusplus
 const MojoHandle MOJO_HANDLE_INVALID = 0;
@@ skipping 146 matching lines @@
 // 32-bit-aligned.
 MOJO_STATIC_ASSERT(MOJO_ALIGNOF(int32_t) == 4, "int32_t has weird alignment");
 struct MOJO_ALIGNAS(4) MojoHandleSignalsState {
   MojoHandleSignals satisfied_signals;
   MojoHandleSignals satisfiable_signals;
 };
 MOJO_STATIC_ASSERT(sizeof(MojoHandleSignalsState) == 8,
                    "MojoHandleSignalsState has wrong size");
 
 #endif  // MOJO_PUBLIC_C_SYSTEM_TYPES_H_