Add UMA histograms for the inter-process TimeTicks skew.

content/common/inter_process_time_ticks_converter.cc

Index: content/common/inter_process_time_ticks_converter.cc
diff --git a/content/common/inter_process_time_ticks_converter.cc b/content/common/inter_process_time_ticks_converter.cc
index de3fb13d9913d54f06136406bb3c095982edb358..e0c12e2bba34a9698ec9263c2acb25df7e7abbbe 100644
--- a/content/common/inter_process_time_ticks_converter.cc
+++ b/content/common/inter_process_time_ticks_converter.cc
@@ -72,4 +72,13 @@ int64 InterProcessTimeTicksConverter::Convert(int64 value) const {
   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