Adding local field trial for metrics/crash reports sampling.

chrome/browser/chrome_browser_field_trials.h

Index: chrome/browser/chrome_browser_field_trials.h
diff --git a/chrome/browser/chrome_browser_field_trials.h b/chrome/browser/chrome_browser_field_trials.h
index f8c6fea4f4ffecb7122f937e9de03d2465cb814d..f57caa7df27fcdbdb9164e582fed12a42c1805fd 100644
--- a/chrome/browser/chrome_browser_field_trials.h
+++ b/chrome/browser/chrome_browser_field_trials.h
@@ -9,6 +9,7 @@
 #include "base/macros.h"
 
 namespace base {
+class FeatureList;
 class Time;
 }
 
@@ -19,6 +20,12 @@ class 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.