Minor fixes in FieldTrial.

- Add a DCHECK
- Comment what the return value is on AddGroup
- const a member
- Typo fix

BUG=None
TEST=None

Review URL: http://codereview.chromium.org/6577038

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@76061 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 4 insertions, 2 deletions

diff --git a/base/metrics/field_trial.cc b/base/metrics/field_trial.cc
index fceccde..c1416db 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;
diff --git a/base/metrics/field_trial.h b/base/metrics/field_trial.h
index ec3a483..8b4a6069 100644
--- a/base/metrics/field_trial.h
+++ b/base/metrics/field_trial.h
@@ -101,6 +101,7 @@ class FieldTrial : public RefCounted<FieldTrial> {
   // Establish the name and probability of the next group in this trial.
   // Sometimes, based on construction randomization, this call may cause the
   // provided group to be *THE* group selected for use in this instance.
+  // The return value is the group number of the new group.
   int AppendGroup(const std::string& name, Probability group_probability);
 
   // Return the name of the FieldTrial (excluding the group name).
@@ -167,7 +168,7 @@ class FieldTrial : public RefCounted<FieldTrial> {
   // The randomly selected probability that is used to select a group (or have
   // the instance not participate).  It is the product of divisor_ and a random
   // number between [0, 1).
-  Probability random_;
+  const Probability random_;
 
   // Sum of the probabilities of all appended groups.
   Probability accumulated_group_probability_;