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..6f0ff1f87c865a5ddaa587a9c2d7c10ac50613ff 100644
--- a/components/flags_ui/flags_state.h
+++ b/components/flags_ui/flags_state.h
@@ -21,6 +21,13 @@ class ListValue;
 
 namespace flags_ui {
 
+// Internal functionality exposed for tests.
+namespace internal {
+// The trial group selected when feature variation parameters are registered via
+// FlagsState::RegisterFeatureVariationParameters().
+extern const char kTrialGroupAboutFlags[];
+}  // namespace internal
+
 struct FeatureEntry;
 class FlagsStorage;
 struct SwitchEntry;
@@ -56,6 +63,9 @@ 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 +80,10 @@ 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|.