Record field-trial information in stability file for crash analysis.

base/metrics/field_trial.cc

Index: base/metrics/field_trial.cc
diff --git a/base/metrics/field_trial.cc b/base/metrics/field_trial.cc
index 75832654facebcfa48b91c3fcdffd6caf8a44aa9..ef2f8b756f80fba07e929b8972368cc3fdc1c67c 100644
--- a/base/metrics/field_trial.cc
+++ b/base/metrics/field_trial.cc
@@ -10,6 +10,7 @@
 #include "base/base_switches.h"
 #include "base/build_time.h"
 #include "base/command_line.h"
+#include "base/debug/activity_tracker.h"
 #include "base/logging.h"
 #include "base/metrics/field_trial_param_associator.h"
 #include "base/process/memory.h"
@@ -982,6 +983,11 @@ void FieldTrialList::NotifyFieldTrialGroupSelection(FieldTrial* field_trial) {
       ActivateFieldTrialEntryWhileLocked(field_trial);
   }
 
+  // Recording for stability debugging has to be done inline as a task posted
+  // to an observer may not get executed before a crash.

[Alexei Svitkine (slow), 2017/02/06 17:46:12]

While you're changing this, how about setting crash_keys from the same place?
This way, the problem will also be fixed there too.

[manzagop (departed), 2017/02/06 18:38:16]

IIUC the problem with crash keys is the update leads to querying for all active
experiments, hashing them, and formatting them, which is deemed too expensive to
be inline experiment activation?

[bcwhite, 2017/02/07 15:58:58]

Happy to do it, if it's desired, but I'll do it as a separate CL so if there is
a problem and it has to be reverted, it won't affect the rest.

+  base::debug::GlobalActivityTracker::RecordFieldTrial(

[Alexei Svitkine (slow), 2017/02/06 17:46:12]

Is this API thread safe? Because this can be called from any thread....

If it is, please document it in the API's function comment.

[bcwhite, 2017/02/07 15:58:59]

Yes.  Done.

+      field_trial->trial_name(), field_trial->group_name_internal());
+
   global_->observer_list_->Notify(
       FROM_HERE, &FieldTrialList::Observer::OnFieldTrialGroupFinalized,
       field_trial->trial_name(), field_trial->group_name_internal());