Even more instrumentation to diagnose an Android render crash.

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 78862fa683520bc5d96764e093d7fce54386e12a..364674f54e3cbd22becebecb6c7af7d0a63149b6 100644
--- a/base/metrics/field_trial.cc
+++ b/base/metrics/field_trial.cc
@@ -7,6 +7,7 @@
 #include <algorithm>
 
 #include "base/build_time.h"
+#include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/rand_util.h"
 #include "base/strings/string_util.h"
@@ -115,6 +116,17 @@ void CheckTrialGroup(const std::string& trial_name,
   }
 }
 
+// A second copy of FieldTrialList::seen_states_ that is meant to outlive the
+// FieldTrialList object to determine if the inconsistency happens because there
+// might be multiple FieldTrialList objects.
+// TODO(asvitkine): Remove when crbug.com/359406 is resolved.
+base::LazyInstance<std::map<std::string, std::string>>::Leaky g_seen_states =
+    LAZY_INSTANCE_INITIALIZER;
+
+// Tracks whether |g_seen_states| is used. Defaults to false, because unit tests
+// will create multiple FieldTrialList instances.
+bool g_use_global_check_states = false;
+
 }  // namespace
 
 // statics
@@ -338,6 +350,12 @@ FieldTrialList::~FieldTrialList() {
 }
 
 // static
+void FieldTrialList::EnableGlobalStateChecks() {
+  CHECK(!g_use_global_check_states);
+  g_use_global_check_states = true;
+}
+
+// static
 FieldTrial* FieldTrialList::FactoryGetFieldTrial(
     const std::string& trial_name,
     FieldTrial::Probability total_probability,
@@ -491,6 +509,10 @@ void FieldTrialList::AllStatesToString(std::string* output) {
 
     CheckTrialGroup(trial.trial_name.as_string(), trial.group_name.as_string(),
                     &global_->seen_states_);
+    if (g_use_global_check_states) {
+      CheckTrialGroup(trial.trial_name.as_string(),
+                      trial.group_name.as_string(), &g_seen_states.Get());
+    }
   }
 }
 
@@ -619,6 +641,10 @@ void FieldTrialList::NotifyFieldTrialGroupSelection(FieldTrial* field_trial) {
     AutoLock auto_lock(global_->lock_);
     CheckTrialGroup(field_trial->trial_name(),
                     field_trial->group_name_internal(), &global_->seen_states_);
+    if (g_use_global_check_states) {

[Nico, 2016/04/15 19:00:31]

should this block have a comment too?

[Alexei Svitkine (slow), 2016/04/15 20:28:45]

Done.

+      CheckTrialGroup(field_trial->trial_name(),
+                      field_trial->group_name_internal(), &g_seen_states.Get());
+    }
   }
   global_->observer_list_->Notify(
       FROM_HERE, &FieldTrialList::Observer::OnFieldTrialGroupFinalized,