Add support for the control group in the Simple Cache Experiment.

net/disk_cache/backend_impl.cc

Index: net/disk_cache/backend_impl.cc
diff --git a/net/disk_cache/backend_impl.cc b/net/disk_cache/backend_impl.cc
index fed0546fc00daa6e96c29b24d293d4c0407b72b1..ce2aafde001c4936e1d271ed5d04b5ce33d6fc0b 100644
--- a/net/disk_cache/backend_impl.cc
+++ b/net/disk_cache/backend_impl.cc
@@ -76,13 +76,23 @@ size_t GetIndexSize(int table_len) {
 
 // Sets group for the current experiment. Returns false if the files should be
 // discarded.
-bool InitExperiment(disk_cache::IndexHeader* header) {
+bool InitExperiment(disk_cache::IndexHeader* header, bool cache_created) {
   if (header->experiment == disk_cache::EXPERIMENT_OLD_FILE1 ||
       header->experiment == disk_cache::EXPERIMENT_OLD_FILE2) {
     // Discard current cache.
     return false;
   }
 
+  if (base::FieldTrialList::FindFullName("SimpleCacheTrial") ==
+          "ExperimentControl") {
+    if (cache_created) {
+      header->experiment = disk_cache::EXPERIMENT_SIMPLE_CONTROL;
+      return true;
+    } else if (header->experiment != disk_cache::EXPERIMENT_SIMPLE_CONTROL) {
+      return false;
+    }
+  }
+
   header->experiment = disk_cache::NO_EXPERIMENT;
   return true;
 }
@@ -258,9 +268,10 @@ int BackendImpl::SyncInit() {
   if (!restarted_ && (create_files || !data_->header.num_entries))
     ReportError(ERR_CACHE_CREATED);
 
-  if (!(user_flags_ & kNoRandom) &&
-      cache_type_ == net::DISK_CACHE && !InitExperiment(&data_->header))
+  if (!(user_flags_ & kNoRandom) && cache_type_ == net::DISK_CACHE &&
+      !InitExperiment(&data_->header, create_files)) {
     return net::ERR_FAILED;
+  }
 
   // We don't care if the value overflows. The only thing we care about is that
   // the id cannot be zero, because that value is used as "not dirty".