Added a marker for field trials passed on the command line to force their activation.

BUG=430233

Review URL: https://codereview.chromium.org/700933002

Cr-Commit-Position: refs/heads/master@{#302813}

3 files changed, 47 insertions, 6 deletions

diff --git a/base/metrics/field_trial.cc b/base/metrics/field_trial.cc
index c82f33d..7efca7a3 100644
--- a/base/metrics/field_trial.cc
+++ b/base/metrics/field_trial.cc
@@ -67,6 +67,7 @@ const int FieldTrial::kDefaultGroupNumber = 0;
 bool FieldTrial::enable_benchmarking_ = false;
 
 const char FieldTrialList::kPersistentStringSeparator('/');
+const char FieldTrialList::kActivationMarker('*');
 int FieldTrialList::kNoExpirationYear = 0;
 
 //------------------------------------------------------------------------------
@@ -421,7 +422,18 @@ bool FieldTrialList::CreateTrialsFromString(
       return false;
     if (group_name_end == trials_string.npos)
       group_name_end = trials_string.length();
-    std::string name(trials_string, next_item, name_end - next_item);
+
+    // Verify if the trial should be activated or not.
+    std::string name;
+    bool force_activation = false;
+    if (trials_string[next_item] == kActivationMarker) {
+      // Name cannot be only the indicator.
+      if (name_end - next_item == 1)
+        return false;
+      next_item++;
+      force_activation = true;
+    }
+    name.append(trials_string, next_item, name_end - next_item);
     std::string group_name(trials_string, name_end + 1,
                            group_name_end - name_end - 1);
     next_item = group_name_end + 1;
@@ -432,7 +444,7 @@ bool FieldTrialList::CreateTrialsFromString(
     FieldTrial* trial = CreateFieldTrial(name, group_name);
     if (!trial)
       return false;
-    if (mode == ACTIVATE_TRIALS) {
+    if (mode == ACTIVATE_TRIALS || force_activation) {
       // Call |group()| to mark the trial as "used" and notify observers, if
       // any. This is useful to ensure that field trials created in child
       // processes are properly reported in crash reports.
diff --git a/base/metrics/field_trial.h b/base/metrics/field_trial.h
index 25ee0c1..e2e5439 100644
--- a/base/metrics/field_trial.h
+++ b/base/metrics/field_trial.h
@@ -291,7 +291,8 @@ class BASE_EXPORT FieldTrial : public RefCounted<FieldTrial> {
 class BASE_EXPORT FieldTrialList {
  public:
   // Specifies whether field trials should be activated (marked as "used"), when
-  // created using |CreateTrialsFromString()|.
+  // created using |CreateTrialsFromString()|. Has no effect on trials that are
+  // prefixed with |kActivationMarker|, which will always be activated."
   enum FieldTrialActivationMode {
     DONT_ACTIVATE_TRIALS,
     ACTIVATE_TRIALS,
@@ -302,6 +303,10 @@ class BASE_EXPORT FieldTrialList {
   // second process to mimic our state (i.e., provide the same group name).
   static const char kPersistentStringSeparator;  // Currently a slash.
 
+  // Define a marker character to be used as a prefix to a trial name on the
+  // command line which forces its activation.
+  static const char kActivationMarker;  // Currently an asterisk.
+
   // Year that is guaranteed to not be expired when instantiating a field trial
   // via |FactoryGetFieldTrial()|.  Set to two years from the build date.
   static int kNoExpirationYear;
@@ -412,9 +417,10 @@ class BASE_EXPORT FieldTrialList {
   // used in a non-browser process, to carry randomly selected state in a
   // browser process into this non-browser process, but could also be invoked
   // through a command line argument to the browser process. The created field
-  // trials are marked as "used" for the purposes of active trial reporting if
-  // |mode| is ACTIVATE_TRIALS. Trial names in |ignored_trial_names| are ignored
-  // when parsing |prior_trials|.
+  // trials are all marked as "used" for the purposes of active trial reporting
+  // if |mode| is ACTIVATE_TRIALS, otherwise each trial will be marked as "used"
+  // if it is prefixed with |kActivationMarker|. Trial names in
+  // |ignored_trial_names| are ignored when parsing |prior_trials|.
   static bool CreateTrialsFromString(
       const std::string& prior_trials,
       FieldTrialActivationMode mode,
diff --git a/base/metrics/field_trial_unittest.cc b/base/metrics/field_trial_unittest.cc
index 1ed3f89..ce95c2a 100644
--- a/base/metrics/field_trial_unittest.cc
+++ b/base/metrics/field_trial_unittest.cc
@@ -428,6 +428,12 @@ TEST_F(FieldTrialTest, BogusRestore) {
   EXPECT_FALSE(FieldTrialList::CreateTrialsFromString(
       "noname, only group/", FieldTrialList::DONT_ACTIVATE_TRIALS,
       std::set<std::string>()));
+  EXPECT_FALSE(FieldTrialList::CreateTrialsFromString(
+      "/emptyname", FieldTrialList::DONT_ACTIVATE_TRIALS,
+      std::set<std::string>()));
+  EXPECT_FALSE(FieldTrialList::CreateTrialsFromString(
+      "*/emptyname", FieldTrialList::DONT_ACTIVATE_TRIALS,
+      std::set<std::string>()));
 }
 
 TEST_F(FieldTrialTest, DuplicateRestore) {
@@ -490,6 +496,23 @@ TEST_F(FieldTrialTest, CreateTrialsFromStringNotActive) {
   EXPECT_EQ("zyx", active_groups[1].group_name);
 }
 
+TEST_F(FieldTrialTest, CreateTrialsFromStringForceActivation) {
+  ASSERT_FALSE(FieldTrialList::TrialExists("Abc"));
+  ASSERT_FALSE(FieldTrialList::TrialExists("def"));
+  ASSERT_FALSE(FieldTrialList::TrialExists("Xyz"));
+  ASSERT_TRUE(FieldTrialList::CreateTrialsFromString(
+      "*Abc/cba/def/fed/*Xyz/zyx/", FieldTrialList::DONT_ACTIVATE_TRIALS,
+      std::set<std::string>()));
+
+  FieldTrial::ActiveGroups active_groups;
+  FieldTrialList::GetActiveFieldTrialGroups(&active_groups);
+  ASSERT_EQ(2U, active_groups.size());
+  EXPECT_EQ("Abc", active_groups[0].trial_name);
+  EXPECT_EQ("cba", active_groups[0].group_name);
+  EXPECT_EQ("Xyz", active_groups[1].trial_name);
+  EXPECT_EQ("zyx", active_groups[1].group_name);
+}
+
 TEST_F(FieldTrialTest, CreateTrialsFromStringActiveObserver) {
   ASSERT_FALSE(FieldTrialList::TrialExists("Abc"));