Implement A/B experiment for anti-DDoS.

chrome/common/pref_names.cc

Index: chrome/common/pref_names.cc
diff --git a/chrome/common/pref_names.cc b/chrome/common/pref_names.cc
index 80a07af7e507bf040997b303cc40b6c412810e75..297b2ad9089b2c81f1e59dcd65cef28a0159bfc5 100644
--- a/chrome/common/pref_names.cc
+++ b/chrome/common/pref_names.cc
@@ -691,6 +691,12 @@ const char kPinnedTabs[] = "pinned_tabs";
 // Boolean that is true when HTTP throttling is enabled.
 const char kHttpThrottlingEnabled[] = "http_throttling.enabled";
 
+// Boolean that is true until the user changes the setting of the check-box
+// that controls whether HTTP throttling is enabled. When this is false,
+// we do not allow FieldTrial experiments to modify whether the feature
+// is enabled or not.
+const char kHttpThrottlingMayExperiment[] = "http_throttling.may_experiment";
+
 // Integer containing the default Geolocation content setting.
 const char kGeolocationDefaultContentSetting[] =
     "geolocation.default_content_setting";