Add UMA histograms for the inter-process TimeTicks skew.

content/common/inter_process_time_ticks_converter.cc

 // Copyright (c) 2011 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.
 
 #include "content/common/inter_process_time_ticks_converter.h"
 
 #include "base/logging.h"
 #include "base/strings/string_number_conversions.h"
 
 namespace content {
@@ skipping 54 matching lines @@
   return LocalTimeDelta(Convert(remote_delta.value_));
 }
 
 int64 InterProcessTimeTicksConverter::Convert(int64 value) const {
   if (value <= 0) {
     return value;
   }
   return numerator_ * value / denominator_;
 }
 
+bool InterProcessTimeTicksConverter::IsSkewAdditiveForMetrics() const {
+  return numerator_ == 1 && denominator_ == 1;

[pasko, 2014/08/18 09:30:34]

I guess non-additive cases are assumed to be low, is that right? What can we do
with the data once we get it?

After a quick first glance, the fitting in the Converter does not look very
scientific to me, which makes me wonder if it would skew our skew :) Are
Converters readjusted at some point in time? How many measurements are made to
get *_lower_bound and *_upper_bound before we conclude whether we are additive?

+}
+
+base::TimeDelta InterProcessTimeTicksConverter::GetSkewForMetrics() const {
+  return base::TimeTicks::FromInternalValue(remote_lower_bound_) -
+      base::TimeTicks::FromInternalValue(local_base_time_);
+}
+
 }  // namespace content