Added data reduction proxy holdback experiment

components/data_reduction_proxy/browser/data_reduction_proxy_params.h

Index: components/data_reduction_proxy/browser/data_reduction_proxy_params.h
diff --git a/components/data_reduction_proxy/browser/data_reduction_proxy_params.h b/components/data_reduction_proxy/browser/data_reduction_proxy_params.h
index 549a588a555639588542cffec200c01805431e3c..10a43741c7243cc97663156b539bd83780bb3579 100644
--- a/components/data_reduction_proxy/browser/data_reduction_proxy_params.h
+++ b/components/data_reduction_proxy/browser/data_reduction_proxy_params.h
@@ -28,6 +28,7 @@ class DataReductionProxyParams {
   static const unsigned int kFallbackAllowed = (1 << 1);
   static const unsigned int kAlternativeAllowed = (1 << 2);
   static const unsigned int kPromoAllowed = (1 << 3);
+  static const unsigned int kHoldback = (1 << 4);

[marq (ping after 24h), 2014/07/11 16:41:24]

These flags should have some kind of comments.

[bengr, 2014/07/14 18:51:43]

Done.

 
   typedef std::vector<GURL> DataReductionProxyList;
 
@@ -47,6 +48,10 @@ class DataReductionProxyParams {
   // hinting.
   static bool IsIncludedInPreconnectHintingFieldTrial();
 
+  // Returns true if this client is part of a field trial that runs a holdback
+  // experiment.

[marq (ping after 24h), 2014/07/11 16:41:24]

Define 'holdback experiment', for the benefit of someone reading the code in
nine months without the CL description for context.

[bengr, 2014/07/14 18:51:43]

Done.

+  static bool IsIncludedInHoldbackFieldTrial();
+
   // Constructs configuration parameters. If |kAllowed|, then the standard
   // data reduction proxy configuration is allowed to be used. If
   // |kfallbackAllowed| a fallback proxy can be used if the primary proxy is
@@ -147,6 +152,12 @@ class DataReductionProxyParams {
     return promo_allowed_;
   }
 
+  // Returns true if the data reduction proxy should not actually use the
+  // proxy if enabled.
+  bool holdback() const {
+    return holdback_;
+  }
+
   // Given |allowed_|, |fallback_allowed_|, and |alt_allowed_|, returns the
   // list of data reduction proxies that may be used.
   DataReductionProxyList GetAllowedProxies() const;
@@ -194,6 +205,7 @@ class DataReductionProxyParams {
   const bool fallback_allowed_;
   bool alt_allowed_;
   const bool promo_allowed_;
+  bool holdback_;
 
   bool configured_on_command_line_;