Supporting command line argument to force field trials

base/metrics/field_trial.h

Index: base/metrics/field_trial.h
diff --git a/base/metrics/field_trial.h b/base/metrics/field_trial.h
index 50508d241425e558f4f4d737cf352947a86f0bef..8b87730483f1561dea85634f9ea7dfc8fe4d2d90 100644
--- a/base/metrics/field_trial.h
+++ b/base/metrics/field_trial.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -119,9 +119,10 @@ class BASE_EXPORT FieldTrial : public RefCounted<FieldTrial> {
   // Using this constructor creates a startup-randomized FieldTrial. If you

[Alexei Svitkine (slow), 2012/03/23 18:41:55]

Update this comment, since this is no longer a constructor. Also, please move
the last paragraph to the beginning of the comment since that introduces what
the function does.

[MAD, 2012/03/23 20:20:12]

Done.

   // want a one-time randomized trial, call UseOneTimeRandomization() right
   // after construction.
-  FieldTrial(const std::string& name, Probability total_probability,
-             const std::string& default_group_name, const int year,
-             const int month, const int day_of_month);
+  static FieldTrial* CreateInstance(
+      const std::string& name, Probability total_probability,
+      const std::string& default_group_name, const int year, const int month,
+      const int day_of_month);
 
   // Changes the field trial to use one-time randomization, i.e. produce the
   // same result for the current trial on every run of this client. Must be
@@ -156,8 +157,8 @@ class BASE_EXPORT FieldTrial : public RefCounted<FieldTrial> {
 
   // Gets the unique identifier of the Field Trial, but only if a group was
   // officially chosen, otherwise name_group_id is left untouched and false
-  // is returned. When true is returned, the name and group ids were successfuly
-  // set in name_group_id.
+  // is returned. When true is returned, the name and group ids were
+  // successfully set in name_group_id.
   bool GetNameGroupId(NameGroupId* name_group_id);
 
   // Return the default group name of the FieldTrial.
@@ -193,6 +194,9 @@ class BASE_EXPORT FieldTrial : public RefCounted<FieldTrial> {
 
   friend class RefCounted<FieldTrial>;
 
+  FieldTrial(const std::string& name, Probability total_probability,
+             const std::string& default_group_name, const int year,
+             const int month, const int day_of_month);
   virtual ~FieldTrial();
 
   // Returns the group_name. A winner need not have been chosen.
@@ -247,6 +251,9 @@ class BASE_EXPORT FieldTrial : public RefCounted<FieldTrial> {
   // group.
   bool enable_field_trial_;
 
+  // When forced_ is true, we relaxed some of the checks for double init.
+  bool forced_;
+
   // When benchmarking is enabled, field trials all revert to the 'default'
   // group.
   static bool enable_benchmarking_;
@@ -263,7 +270,7 @@ class BASE_EXPORT FieldTrial : public RefCounted<FieldTrial> {
 // Only one instance of this class exists.
 class BASE_EXPORT FieldTrialList {
  public:
-  // Define a separator charactor to use when creating a persistent form of an
+  // Define a separator character to use when creating a persistent form of an
   // instance.  This is intended for use as a command line argument, passed to a
   // second process to mimic our state (i.e., provide the same group name).
   static const char kPersistentStringSeparator;  // Currently a slash.
@@ -292,10 +299,6 @@ class BASE_EXPORT FieldTrialList {
   // Destructor Release()'s references to all registered FieldTrial instances.
   ~FieldTrialList();
 
-  // Register() stores a pointer to the given trial in a global map.
-  // This method also AddRef's the indicated trial.
-  static void Register(FieldTrial* trial);
-
   // The Find() method can be used to test to see if a named Trial was already
   // registered, or to retrieve a pointer to it from the global map.
   static FieldTrial* Find(const std::string& name);
@@ -311,11 +314,12 @@ class BASE_EXPORT FieldTrialList {
   // Returns true if the named trial has been registered.
   static bool TrialExists(const std::string& name);
 
-  // Create a persistent representation of all FieldTrial instances and the
-  // |client_id()| state for resurrection in another process.  This allows
-  // randomization to be done in one process, and secondary processes can be
-  // synchronized on the result. The resulting string contains the
-  // |client_id()|, the names, the trial name, and a "/" separator.
+  // Creates a persistent representation of all FieldTrial instances for
+  // resurrection in another process. This allows randomization to be done in
+  // one process, and secondary processes can be synchronized on the result.
+  // The resulting string contains the name and group name pairs for all trials,
+  // with "/" used to separate all names and to terminate the string. This
+  // string is parsed by CreateTrialsFromString().
   static void StatesToString(std::string* output);
 
   // Returns an array of Unique IDs for each Field Trial that has a chosen
@@ -324,16 +328,13 @@ class BASE_EXPORT FieldTrialList {
   static void GetFieldTrialNameGroupIds(
       std::vector<FieldTrial::NameGroupId>* name_group_ids);
 
-  // Use a previously generated state string (re: StatesToString()) augment the
-  // current list of field tests to include the supplied tests, and using a 100%
-  // probability for each test, force them to have the same group string.  This
-  // is commonly used in a non-browser process, to carry randomly selected state
-  // in a browser process into this non-browser process. This method calls
-  // CreateFieldTrial to create the FieldTrial in the non-browser process.
-  // Currently only the group_name_ and name_ are restored, as well as the
-  // |client_id()| state, that could be used for one-time randomized trials
-  // set up only in child processes.
-  static bool CreateTrialsInChildProcess(const std::string& prior_trials);
+  // Use a state string (re: StatesToString()) to augment the current list of
+  // field tests to include the supplied tests, and using a 100% probability for
+  // each test, force them to have the same group string.  This is commonly used
+  // in a non-browser process, to carry randomly selected state in a browser
+  // process into this non-browser process, but could also be invoked through a
+  // command line argument to the browser process.
+  static bool CreateTrialsFromString(const std::string& prior_trials);
 
   // Create a FieldTrial with the given |name| and using 100% probability for
   // the FieldTrial, force FieldTrial to have the same group string as
@@ -384,12 +385,19 @@ class BASE_EXPORT FieldTrialList {
   static const std::string& client_id();
 
  private:
+  friend class base::FieldTrial;
+
   // A map from FieldTrial names to the actual instances.
   typedef std::map<std::string, FieldTrial*> RegistrationList;
 
   // Helper function should be called only while holding lock_.
   FieldTrial* PreLockedFind(const std::string& name);
 
+  // Register() stores a pointer to the given trial in a global map.
+  // This method also AddRef's the indicated trial.
+  // This should only be called by FieldTrial::CreateInstance.
+  static void Register(FieldTrial* trial);
+
   static FieldTrialList* global_;  // The singleton of this class.
 
   // This will tell us if there is an attempt to register a field