Set exp id in the CP header if user is in Lo-Fi control.

components/data_reduction_proxy/core/browser/data_reduction_proxy_request_options.cc

Index: components/data_reduction_proxy/core/browser/data_reduction_proxy_request_options.cc
diff --git a/components/data_reduction_proxy/core/browser/data_reduction_proxy_request_options.cc b/components/data_reduction_proxy/core/browser/data_reduction_proxy_request_options.cc
index 24be61b0998bdf0d2ccf1d351a23bc011451d626..4bfc8ece5c13d3ac870b280b95df133f8afdc5b1 100644
--- a/components/data_reduction_proxy/core/browser/data_reduction_proxy_request_options.cc
+++ b/components/data_reduction_proxy/core/browser/data_reduction_proxy_request_options.cc
@@ -4,6 +4,7 @@
 
 #include "components/data_reduction_proxy/core/browser/data_reduction_proxy_request_options.h"
 
+#include <algorithm>
 #include <vector>
 
 #include "base/bind.h"
@@ -49,6 +50,7 @@ const char kPatchNumberHeaderOption[] = "p";
 const char kClientHeaderOption[] = "c";
 const char kLoFiHeaderOption[] = "q";
 const char kExperimentsOption[] = "exp";
+const char kLoFiExperimentID[] = "LoFiControl";
 
 // The empty version for the authentication protocol. Currently used by
 // Android webview.
@@ -169,33 +171,49 @@ void DataReductionProxyRequestOptions::MayRegenerateHeaderBasedOnLoFi(
       !(request && request->load_flags() & net::LOAD_BYPASS_CACHE) &&
       data_reduction_proxy_config_->ShouldUseLoFiHeaderForRequests();
 
-  // Lo-Fi was not enabled, but now is. Add the header option.
+  bool regenerate = false;

[megjablon, 2015/10/01 18:54:44]

Do we need this? It's more lines than just calling
RegenerateRequestHeaderValue() when we set regenerate = true;

[tbansal1, 2015/10/02 16:50:43]

Done.

+
   if (lofi_.empty() && lofi_now_enabled) {
+    // Lo-Fi was not enabled, but now is. Add the header option.
     lofi_ = "low";
-    RegenerateRequestHeaderValue();
-    return;
+    regenerate = true;
+  } else if (!lofi_.empty() && !lofi_now_enabled) {
+    // Lo-Fi was enabled, but no longer is. Remove the header option.
+    lofi_ = std::string();
+    regenerate = true;
+  } else if (std::find(experiments_.begin(), experiments_.end(),
+                       std::string(kLoFiExperimentID)) == experiments_.end() &&
+             data_reduction_proxy_config_->IsInLoFiControlExperiment()) {
+    // User was not part of Lo-Fi control experiment, but now is.

[megjablon, 2015/10/01 18:54:44]

We also need the case where the user is part of the active control experiment
and then isn't anymore which removes the experiment. 

Also, can we use IsInLoFiActiveControlExperiment instead? Otherwise it just
sounds like we're checking the field trial value.

[tbansal1, 2015/10/02 16:50:42]

Done.

+    experiments_.push_back(kLoFiExperimentID);
+    regenerate = true;
   }
 
-  // Lo-Fi was enabled, but no longer is. Remove the header option.
-  if (!lofi_.empty() && !lofi_now_enabled) {
-    lofi_ = std::string();
+  if (regenerate)
     RegenerateRequestHeaderValue();
-    return;
-  }
+  DCHECK_IMPLIES(data_reduction_proxy_config_->IsInLoFiControlExperiment(),
+                 std::find(experiments_.begin(), experiments_.end(),
+                           kLoFiExperimentID) != experiments_.end());
 }
 
 void DataReductionProxyRequestOptions::UpdateExperiments() {
+  experiments_.clear();

[megjablon, 2015/10/01 18:54:44]

Why is this needed? This is only called on initialization so there shouldn't be
any experiments yet.

[tbansal1, 2015/10/02 16:50:43]

Done.

   std::string experiments =
       base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
           data_reduction_proxy::switches::kDataReductionProxyExperiment);
-  if (experiments.empty())
+  if (experiments.empty() &&
+      !data_reduction_proxy_config_->IsInLoFiControlExperiment()) {
     return;
+  }

[megjablon, 2015/10/01 18:54:44]

UpdateExperiments() is only called from Init(). Do we need to worry about the
Lo-Fi control experiment in UpdateExperiments() since it will be updated on the
first call to MaybeAddRequestHeader().

[tbansal1, 2015/10/02 16:50:43]

Done.

   base::StringTokenizer experiment_tokenizer(experiments, ", ");
   experiment_tokenizer.set_quote_chars("\"");
   while (experiment_tokenizer.GetNext()) {
     if (!experiment_tokenizer.token().empty())
       experiments_.push_back(experiment_tokenizer.token());
   }
+  if (data_reduction_proxy_config_->IsInLoFiControlExperiment())
+    experiments_.push_back(kLoFiExperimentID);
+
   RegenerateRequestHeaderValue();
 }