Fix getting initially active trials with shared memory.

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 8ec56b8a59e340763a371c38a921ce779d11f4dc..b1206f7f133c34bc33be3af43faf8382a6d83430 100644
--- a/base/metrics/field_trial.cc
+++ b/base/metrics/field_trial.cc
@@ -625,6 +625,40 @@ void FieldTrialList::GetActiveFieldTrialGroupsFromString(
 }
 
 // static
+void FieldTrialList::GetInitiallyActiveFieldTrials(
+    const base::CommandLine& command_line,
+    FieldTrial::ActiveGroups* active_groups) {
+  DCHECK(global_->create_trials_from_command_line_called_);

[lawrencewu, 2016/11/18 16:33:10]

This function is called or can be called before CreateTrialsFromCommandLine().
Does this have to be called after it? Getting the active groups and creating the
trials seems independent from each other.

[Alexei Svitkine (slow), 2016/11/18 16:35:47]

If it's called before it, then the field_trial_allocator_ won't be created yet.
So it needs to be called after.

I will take a look at why the order isn't what I expected.

+
+  if (!global_->field_trial_allocator_) {
+    GetActiveFieldTrialGroupsFromString(
+        command_line.GetSwitchValueASCII(switches::kForceFieldTrials),
+        active_groups);
+    return;
+  }
+
+  SharedPersistentMemoryAllocator* allocator =
+      global_->field_trial_allocator_.get();
+  PersistentMemoryAllocator::Iterator mem_iter(allocator);
+  SharedPersistentMemoryAllocator::Reference ref;
+  while ((ref = mem_iter.GetNextOfType(kFieldTrialType)) !=
+         SharedPersistentMemoryAllocator::kReferenceNull) {
+    const FieldTrialEntry* entry =
+        allocator->GetAsObject<const FieldTrialEntry>(ref, kFieldTrialType);
+
+    StringPiece trial_name;
+    StringPiece group_name;
+    if (entry->activated &&
+        entry->GetTrialAndGroupName(&trial_name, &group_name)) {
+      FieldTrial::ActiveGroup group;
+      group.trial_name = trial_name.as_string();
+      group.group_name = group_name.as_string();
+      active_groups->push_back(group);

[bcwhite, 2016/11/21 15:56:22]

push_back(std::move(group))

[Alexei Svitkine (slow), 2016/11/21 20:47:11]

Done.

+    }
+  }
+}
+
+// static
 bool FieldTrialList::CreateTrialsFromString(
     const std::string& trials_string,
     const std::set<std::string>& ignored_trial_names) {
@@ -660,7 +694,7 @@ bool FieldTrialList::CreateTrialsFromString(
 void FieldTrialList::CreateTrialsFromCommandLine(
     const CommandLine& cmd_line,
     const char* field_trial_handle_switch) {
-  DCHECK(global_);
+  global_->create_trials_from_command_line_called_ = true;
 
 #if defined(OS_WIN) && !defined(OS_NACL)
   if (cmd_line.HasSwitch(field_trial_handle_switch)) {