Remove a DCHECK() in FieldTrial::SetForced().

The DCHECK() was added under the assumption that it doesn't
make sense to force a trial that only has the default group.

However, with VariationsService, which is general-purpose,
one could create a server-side trial of this sort, and this
works correctly other than the DCHECK().

BUG=160766
TEST=New unit tests in field_trial_unittest.cc.
Review URL: https://codereview.chromium.org/11366205

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@167453 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 36 insertions, 4 deletions

diff --git a/base/metrics/field_trial.cc b/base/metrics/field_trial.cc
index 3a563aa..458ff4d 100644
--- a/base/metrics/field_trial.cc
+++ b/base/metrics/field_trial.cc
@@ -178,10 +178,6 @@ void FieldTrial::SetForced() {
   // first come first served, e.g., command line switch has precedence.
   if (forced_)
     return;
-  // Explicit forcing should only be for cases where we want to set the group
-  // probabilities before the hard coded field trial setup is executed. So
-  // there must have been at least one non-default group appended at that point.
-  DCHECK_GT(next_group_number_, kDefaultGroupNumber + 1);
 
   // And we must finalize the group choice before we mark ourselves as forced.
   FinalizeGroupChoice();
diff --git a/base/metrics/field_trial_unittest.cc b/base/metrics/field_trial_unittest.cc
index 1ab8467..a77b5ef 100644
--- a/base/metrics/field_trial_unittest.cc
+++ b/base/metrics/field_trial_unittest.cc
@@ -588,6 +588,42 @@ TEST_F(FieldTrialTest, SetForced) {
   EXPECT_EQ(forced_group, would_win_group);
 }
 
+TEST_F(FieldTrialTest, SetForcedDefaultOnly) {
+  const char kTrialName[] = "SetForcedDefaultOnly";
+  ASSERT_FALSE(FieldTrialList::TrialExists(kTrialName));
+
+  int default_group = -1;
+  FieldTrial* trial =
+      FieldTrialList::FactoryGetFieldTrial(kTrialName, 100, kDefaultGroupName,
+                                           next_year_, 12, 31, &default_group);
+  trial->SetForced();
+
+  trial = FieldTrialList::FactoryGetFieldTrial(kTrialName, 100,
+                                               kDefaultGroupName, next_year_,
+                                               12, 31, NULL);
+  EXPECT_EQ(default_group, trial->group());
+  EXPECT_EQ(kDefaultGroupName, trial->group_name());
+}
+
+TEST_F(FieldTrialTest, SetForcedDefaultWithExtraGroup) {
+  const char kTrialName[] = "SetForcedDefaultWithExtraGroup";
+  ASSERT_FALSE(FieldTrialList::TrialExists(kTrialName));
+
+  int default_group = -1;
+  FieldTrial* trial =
+      FieldTrialList::FactoryGetFieldTrial(kTrialName, 100, kDefaultGroupName,
+                                           next_year_, 12, 31, &default_group);
+  trial->SetForced();
+
+  trial = FieldTrialList::FactoryGetFieldTrial(kTrialName, 100,
+                                               kDefaultGroupName, next_year_,
+                                               12, 31, NULL);
+  const int extra_group = trial->AppendGroup("Extra", 100);
+  EXPECT_EQ(default_group, trial->group());
+  EXPECT_NE(extra_group, trial->group());
+  EXPECT_EQ(kDefaultGroupName, trial->group_name());
+}
+
 TEST_F(FieldTrialTest, Observe) {
   const char kTrialName[] = "TrialToObserve1";
   const char kSecondaryGroupName[] = "SecondaryGroup";