Do not record CPU profile samples when stack collection is failed.

src/profiler/cpu-profiler.cc

Index: src/profiler/cpu-profiler.cc
diff --git a/src/profiler/cpu-profiler.cc b/src/profiler/cpu-profiler.cc
index b6c7945797bc702cb647c5de58195f90ff6ae967..5252b9363a718380c36695224ca94f8dbce71da7 100644
--- a/src/profiler/cpu-profiler.cc
+++ b/src/profiler/cpu-profiler.cc
@@ -114,7 +114,9 @@ ProfilerEventsProcessor::SampleProcessingResult
   if (record->order != last_processed_code_event_id_) {
     return FoundSampleForNextCodeEvent;
   }
-  generator_->RecordTickSample(record->sample);
+  if (record->sample.pc) {

[titzer, 2016/02/19 09:28:37]

Will this tick just be discarded? Is there a bucket for discarded ticks to avoid
showing skewed results?

[alph, 2016/02/19 16:24:29]

It is just discarded, so effectively it adds to all other samples a bit.
There's no such a bucket. If I add one I'm not sure how that would be presented
to the user.
Actually currently the results are skewed as well because if we fail to collect
a stack the sample is not attributed to the function currently being executed,
but to a program node instead. So the function node becomes smaller than it is
in the reality.

[titzer, 2016/02/19 16:36:33]

As long as the missing samples go somewhere, so as not to skew the existing
samples, then this sgtm.

[alph, 2016/02/19 17:54:22]

Agree.

+    generator_->RecordTickSample(record->sample);
+  }
   ticks_buffer_.Remove();
   return OneSampleProcessed;
 }