Store and retrieve features from shared memory

base/metrics/field_trial.h

 // Copyright (c) 2012 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.
 
 // FieldTrial is a class for handling details of statistical experiments
 // performed by actual users in the field (i.e., in a shipped or beta product).
 // All code is called exclusively on the UI thread currently.
 //
 // The simplest example is an experiment to see whether one of two options
 // produces "better" results across our user population.  In that scenario, UMA
@@ skipping 47 matching lines @@
 #include <stdint.h>
 
 #include <map>
 #include <memory>
 #include <set>
 #include <string>
 #include <vector>
 
 #include "base/base_export.h"
 #include "base/command_line.h"
+#include "base/feature_list.h"
 #include "base/files/file.h"
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/shared_memory.h"
 #include "base/metrics/persistent_memory_allocator.h"
 #include "base/observer_list_threadsafe.h"
 #include "base/process/launch.h"
 #include "base/strings/string_piece.h"
 #include "base/synchronization/lock.h"
@@ skipping 423 matching lines @@
   // handle or command line argument. A bit of a misnomer since on POSIX we
   // simply get the trials from opening |fd_key| if using shared memory. On
   // Windows, we expect the |cmd_line| switch for |field_trial_handle_switch| to
   // contain the shared memory handle that contains the field trial allocator.
   // We need the |field_trial_handle_switch| and |fd_key| arguments to be passed
   // in since base/ can't depend on content/.
   static void CreateTrialsFromCommandLine(const base::CommandLine& cmd_line,
                                           const char* field_trial_handle_switch,
                                           int fd_key);
 
+  // Creates base::Feature overrides from the command line by first trying to
+  // use shared memory and then falling back to the command line if it fails.
+  static void CreateFeaturesFromCommandLine(
+      const base::CommandLine& command_line,
+      const char* enable_features_switch,
+      const char* disable_features_switch,
+      FeatureList* feature_list);
+
 #if defined(OS_WIN)
   // On Windows, we need to explicitly pass down any handles to be inherited.
   // This function adds the shared memory handle to field trial state to the
   // list of handles to be inherited.
   static void AppendFieldTrialHandleIfNeeded(
       base::HandlesToInheritVector* handles);
 #elif defined(OS_POSIX)
   // On POSIX, we also need to explicitly pass down this file descriptor that
   // should be shared with the child process. Returns kInvalidPlatformFile if no
   // handle exists or was not initialized properly.
   static PlatformFile GetFieldTrialHandle();
 #endif
 
   // Adds a switch to the command line containing the field trial state as a
   // string (if not using shared memory to share field trial state), or the
   // shared memory handle + length.
   // Needs the |field_trial_handle_switch| argument to be passed in since base/
   // can't depend on content/.
   static void CopyFieldTrialStateToFlags(const char* field_trial_handle_switch,
+                                         const char* enable_features_switch,
+                                         const char* disable_features_switch,
                                          base::CommandLine* cmd_line);
 
   // Create a FieldTrial with the given |name| and using 100% probability for
   // the FieldTrial, force FieldTrial to have the same group string as
   // |group_name|. This is commonly used in a non-browser process, to carry
   // randomly selected state in a browser process into this non-browser process.
   // It returns NULL if there is a FieldTrial that is already registered with
   // the same |name| but has different finalized group string (|group_name|).
   static FieldTrial* CreateFieldTrial(const std::string& name,
                                       const std::string& group_name);
@@ skipping 124 matching lines @@
 
   // Tracks whether CreateTrialsFromCommandLine() has been called.
   bool create_trials_from_command_line_called_ = false;
 
   DISALLOW_COPY_AND_ASSIGN(FieldTrialList);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_FIELD_TRIAL_H_