[Feature Switch][Media Router] Add required field trials to MR switch.

extensions/common/feature_switch.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef EXTENSIONS_COMMON_FEATURE_SWITCH_H_
 #define EXTENSIONS_COMMON_FEATURE_SWITCH_H_
 
 #include <string>
+#include <vector>
 
 #include "base/macros.h"
 
 namespace base {
 class CommandLine;
 }
 
 namespace extensions {
 
 // A switch that can turn a feature on or off. Typically controlled via
 // command-line switches but can be overridden, e.g., for testing.
 // Can also integrate with Finch's field trials.
 // A note about priority:
 // 1. If an override is present, the override state will be used.
 // 2. If there is no switch name, the default value will be used. This is
 //    because certain features are specifically designed *not* to be able to
 //    be turned off via command-line, so we can't consult it (or, by extension,
 //    the finch config).
 // 3. If there is a switch name, and the switch is present in the command line,
 //    the command line value will be used.
 // 4. If there is a finch experiment associated and applicable to the machine,
-//    the finch value will be used.
+//    the finch value will be used. In order for the feature to be enabled by
+//    finch experiment, the machine must be in the "Enabled" group for the
+//    experiment and all dependent experiments.
 // 5. Otherwise, the default value is used.
 class FeatureSwitch {
  public:
   static FeatureSwitch* easy_off_store_install();
   static FeatureSwitch* force_dev_mode_highlighting();
   static FeatureSwitch* prompt_for_external_extensions();
   static FeatureSwitch* error_console();
   static FeatureSwitch* enable_override_bookmarks_ui();
   static FeatureSwitch* extension_action_redesign();
   static FeatureSwitch* scripts_require_action();
@@ skipping 24 matching lines @@
     DISALLOW_COPY_AND_ASSIGN(ScopedOverride);
   };
 
   // |switch_name| can be null, in which case the feature is controlled solely
   // by the default and override values.
   FeatureSwitch(const char* switch_name,
                 DefaultValue default_value);
   FeatureSwitch(const char* switch_name,
                 const char* field_trial_name,
                 DefaultValue default_value);
+  FeatureSwitch(const char* switch_name,
+                const char* field_trial_name,
+                const std::vector<const char*>& dependent_field_trials,

[Devlin, 2016/02/09 18:45:14]

"dependent" is the wrong word here - it should probably be "required"

[imcheng, 2016/02/09 21:35:39]

Done.

+                DefaultValue default_value);
   FeatureSwitch(const base::CommandLine* command_line,
                 const char* switch_name,
                 DefaultValue default_value);
   FeatureSwitch(const base::CommandLine* command_line,
                 const char* switch_name,
                 const char* field_trial_name,
+                const std::vector<const char*>& dependent_field_trials,
                 DefaultValue default_value);
+  ~FeatureSwitch();
 
   // Consider using ScopedOverride instead.
   void SetOverrideValue(OverrideValue value);
   OverrideValue GetOverrideValue() const;
 
   bool IsEnabled() const;
 
  private:
   std::string GetLegacyEnableFlag() const;
   std::string GetLegacyDisableFlag() const;
+  bool DependentFieldTrialsEnabled() const;
 
   const base::CommandLine* command_line_;
   const char* switch_name_;
   const char* field_trial_name_;
+  std::vector<const char*> dependent_field_trials_;

[Devlin, 2016/02/09 18:45:14]

this should probably just be std::vector<std::string>

[imcheng, 2016/02/09 21:35:39]

Done.

   bool default_value_;
   OverrideValue override_value_;
 
   DISALLOW_COPY_AND_ASSIGN(FeatureSwitch);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_COMMON_FEATURE_SWITCH_H_