Adding reporting of metrics sampling rate.

components/variations/variations_associated_data.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 COMPONENTS_VARIATIONS_VARIATIONS_ASSOCIATED_DATA_H_
 #define COMPONENTS_VARIATIONS_VARIATIONS_ASSOCIATED_DATA_H_
 
 #include <map>
 #include <string>
 
@@ skipping 135 matching lines @@
 // field trial being marked as active if found (i.e. group() will be called on
 // it), if it wasn't already. Currently, this information is only available from
 // the browser process. Thread safe.
 std::string GetVariationParamValue(const std::string& trial_name,
                                    const std::string& param_name);
 
 // Retrieves a specific parameter value corresponding to |param_name| for the
 // variation associated with the specified |feature|. A feature is associated
 // with at most one variation, through the variation's associated field trial,
 // and selected group. See base/feature_list.h for more information on
-// features. If the feature is not enabled, or if there's no associated
-// variation params, returns false and does not modify |params|. Calling this
-// function will result in the associated field trial being marked as active if
-// found (i.e. group() will be called on it), if it wasn't already. Currently,
-// this information is only available from the browser process. Thread safe.
+// features. If the feature is not enabled, or the specified parameter does not
+// exist, returns an empty string.Calling this function will result in the
+// associated field trial being marked as active if found (i.e. group() will be
+// called on it), if it wasn't already. Currently, this information is only
+// available from the browser process. Thread safe.
 std::string GetVariationParamValueByFeature(const base::Feature& feature,
                                             const std::string& param_name);
 
 // Expose some functions for testing.
 namespace testing {
 
 // Use this class as a member in your test class to set variation params for
 // your tests. You can directly set the parameters in the constructor (if they
 // are used by other members upon construction). You can change them later
 // arbitrarily many times using the SetVariationParams function. Internally, it
@@ skipping 22 matching lines @@
 void ClearAllVariationIDs();
 
 // Clears all of the associated params.
 void ClearAllVariationParams();
 
 }  // namespace testing
 
 }  // namespace variations
 
 #endif  // COMPONENTS_VARIATIONS_VARIATIONS_ASSOCIATED_DATA_H_