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..ecca3f28bf43209fea21c6e7b4dd3b96b3da4029 100644
--- a/components/flags_ui/flags_state.h
+++ b/components/flags_ui/flags_state.h
@@ -50,12 +50,20 @@ enum SentinelsMode { kNoSentinels, kAddSentinels };
 enum FlagAccess { kGeneralAccessFlagsOnly, kOwnerAccessToFlags,
                   kAppleReviewAccessToFlags };
 
+// The trial group selected when feature variation parameters are registered via
+// FlagsState::RegisterFeatureVariationParameters().
+const char kTrialGroupAboutFlags[] = "AboutFlags";
+
 // Stores and encapsulates the little state that about:flags has.
 class FlagsState {
  public:
   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 +78,10 @@ class FlagsState {
   void ResetAllFlags(FlagsStorage* flags_storage);
   void Reset();
 
+  // Registers variations parameter values stored in |flags_storage| (previously
+  // selected in about:flags).
+  void RegisterFeatureVariationParameters(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|.