Specify the trial name when crashing due to missing default group name.

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 6b38d55bbd95f21dd57a5ae2a858277a9e6e9353..dee935fba0144166af81b167041a580737f08c3c 100644
--- a/base/metrics/field_trial.cc
+++ b/base/metrics/field_trial.cc
@@ -414,7 +414,8 @@ FieldTrial::FieldTrial(const std::string& trial_name,
       ref_(FieldTrialList::FieldTrialAllocator::kReferenceNull) {
   DCHECK_GT(total_probability, 0);
   DCHECK(!trial_name_.empty());
-  DCHECK(!default_group_name_.empty());
+  DCHECK(!default_group_name_.empty())
+      << "Trial " << trial_name << " is missing a default group name.";
 }
 
 FieldTrial::~FieldTrial() {}