Minor fixes in FieldTrial.

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 fceccde272ab8f0029807f5fa1fa5c9c8e3b9910..c1416dbce2e80a61bc188104c49780c82b9b57c2 100644
--- a/base/metrics/field_trial.cc
+++ b/base/metrics/field_trial.cc
@@ -41,6 +41,7 @@ FieldTrial::FieldTrial(const std::string& name,
     accumulated_group_probability_(0),
     next_group_number_(kDefaultGroupNumber+1),
     group_(kNotFinalized) {
+  DCHECK_GT(total_probability, 0);
   DCHECK(!default_group_name_.empty());
   FieldTrialList::Register(this);
 
@@ -53,7 +54,7 @@ FieldTrial::FieldTrial(const std::string& name,
   base::Time::Exploded exploded;
   exploded.year = year;
   exploded.month = month;
-  exploded.day_of_week = 0;  // Should be unusued.
+  exploded.day_of_week = 0;  // Should be unused.
   exploded.day_of_month = day_of_month;
   exploded.hour = 0;
   exploded.minute = 0;