Adding local field trial for metrics/crash reports sampling.

chrome/browser/chrome_browser_field_trials.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.
 
 #ifndef CHROME_BROWSER_CHROME_BROWSER_FIELD_TRIALS_H_
 #define CHROME_BROWSER_CHROME_BROWSER_FIELD_TRIALS_H_
 
 #include "base/command_line.h"
 #include "base/macros.h"
 
 namespace base {
+class FeatureList;
 class Time;
 }
 
 class ChromeBrowserFieldTrials {
  public:
   explicit ChromeBrowserFieldTrials(const base::CommandLine& command_line);
   ~ChromeBrowserFieldTrials();
 
   void SetupFieldTrials();
 
+  // Create field trials that will control feature list features. This should be
+  // called during the same timing window as
+  // FeatureList::AssociateReportingFieldTrial.
+  void SetupFeatureControllingFieldTrials(bool was_a_seed_applied,

[Alexei Svitkine (slow), 2016/08/29 19:38:42]

Nit: I find |was_a_seed_applied| name kind of awkward. How about just
|had_seed|. Also, explain the param in the comment.

[jwd, 2016/08/29 21:36:24]

Done.

+                                          base::FeatureList* feature_list);
+
  private:
   // Instantiates dynamic trials by querying their state, to ensure they get
   // reported as used.
   void InstantiateDynamicTrials();
 
   const base::CommandLine& parsed_command_line_;
 
   DISALLOW_COPY_AND_ASSIGN(ChromeBrowserFieldTrials);
 };
 
 #endif  // CHROME_BROWSER_CHROME_BROWSER_FIELD_TRIALS_H_