Support experiment configurations with/without stability metrics.

components/metrics/file_metrics_provider.h

 // Copyright 2016 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_METRICS_FILE_METRICS_PROVIDER_H_
 #define COMPONENTS_METRICS_FILE_METRICS_PROVIDER_H_
 
 #include <list>
 #include <memory>
 #include <string>
@@ skipping 83 matching lines @@
                       SourceType type,
                       SourceAssociation source_association,
                       const base::StringPiece prefs_key);
 
   // Registers all necessary preferences for maintaining persistent state
   // about a monitored file across process restarts. The |prefs_key| is
   // typically the filename.
   static void RegisterPrefs(PrefRegistrySimple* prefs,
                             const base::StringPiece prefs_key);
 
+  // Allow stability metrics support (those found in a file for a previous run
+  // of the browser) to be enabled/disabled. By default it is enabled.
+  static void SetStabilityMetricsEnabled(bool enabled) {
+    stability_metrics_enabled_ = enabled;

[Alexei Svitkine (slow), 2016/11/24 21:27:58]

Nit: Either use hacker_style for the function name or move its body to the .cc.

[bcwhite, 2016/11/25 18:51:58]

Done.

+  }
+
  private:
   friend class FileMetricsProviderTest;
 
   // The different results that can occur accessing a file.
   enum AccessResult {
     // File was successfully mapped.
     ACCESS_RESULT_SUCCESS,
 
     // File does not exist.
     ACCESS_RESULT_DOESNT_EXIST,
@@ skipping 75 matching lines @@
   // they are not subject to the periodic background checking that handles
   // metrics for the current run.
   SourceInfoList sources_for_previous_run_;
 
   // The preferences-service used to store persistent state about sources.
   PrefService* pref_service_;
 
   base::ThreadChecker thread_checker_;
   base::WeakPtrFactory<FileMetricsProvider> weak_factory_;
 
+  // Flag indicating if stability metrics are enabled or disabled.
+  static bool stability_metrics_enabled_;
+
   DISALLOW_COPY_AND_ASSIGN(FileMetricsProvider);
 };
 
 }  // namespace metrics
 
 #endif  // COMPONENTS_METRICS_FILE_METRICS_PROVIDER_H_