Allow overriding variation parameter via chrome://flags.

components/flags_ui/flags_state.h

Index: components/flags_ui/flags_state.h
diff --git a/components/flags_ui/flags_state.h b/components/flags_ui/flags_state.h
index e7d2ac18e2f8062f503b401e1ec083bb1541b8bb..3dbd5a078f28acfc69dd9a366b5b036cd7978b1e 100644
--- a/components/flags_ui/flags_state.h
+++ b/components/flags_ui/flags_state.h
@@ -19,6 +19,12 @@ namespace base {
 class ListValue;
 }
 
+namespace {

[Alexei Svitkine (slow), 2016/06/16 09:40:57]

This is not quite what I meant.

There shouldn't be an anon namespace inside a header file.

Instead, do the following:

// Internal functionality exposed for tests.
namespace internal {
// your comment here
extern const char kTrialGroupAboutFlags[];
}  // namespace internal.

And then define it in the .cc file.

Also, put the above inside of namespace flags_ui.

[jkrcal, 2016/06/16 14:49:17]

Done. 
(Thanks for explaining!)

+// The trial group selected when feature variation parameters are registered via
+// FlagsState::RegisterFeatureVariationParameters().
+const char kTrialGroupAboutFlags[] = "AboutFlags";
+}
+
 namespace flags_ui {
 
 struct FeatureEntry;
@@ -56,6 +62,9 @@ class FlagsState {
   FlagsState(const FeatureEntry* feature_entries, size_t num_feature_entries);
   ~FlagsState();
 
+  // Reads the state from |flags_storage| and adds the command line flags
+  // belonging to the active feature entries to |command_line|. Features are
+  // appended via |enable_features_flag_name| and |disable_features_flag_name|.
   void ConvertFlagsToSwitches(FlagsStorage* flags_storage,
                               base::CommandLine* command_line,
                               SentinelsMode sentinels,
@@ -70,6 +79,10 @@ class FlagsState {
   void ResetAllFlags(FlagsStorage* flags_storage);
   void Reset();
 
+  // Registers variations parameter values stored in |flags_storage| (previously
+  // selected in about:flags).
+  void RegisterAllFeatureVariationParameters(FlagsStorage* flags_storage);
+
   // Gets the list of feature entries. Entries that are available for the
   // current platform are appended to |supported_entries|; all other entries are
   // appended to |unsupported_entries|.