Make SimpleCache the default backend on ChromeOS/Linux.

chrome/browser/profiles/profile_impl_io_data.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/profiles/profile_impl_io_data.h"
 
 #include <memory>
 #include <set>
 #include <string>
 #include <utility>
@@ skipping 70 matching lines @@
   if (command_line.HasSwitch(switches::kUseSimpleCacheBackend)) {
     const std::string opt_value =
         command_line.GetSwitchValueASCII(switches::kUseSimpleCacheBackend);
     if (base::LowerCaseEqualsASCII(opt_value, "off"))
       return net::CACHE_BACKEND_BLOCKFILE;
     if (opt_value.empty() || base::LowerCaseEqualsASCII(opt_value, "on"))
       return net::CACHE_BACKEND_SIMPLE;
   }
   const std::string experiment_name =
       base::FieldTrialList::FindFullName("SimpleCacheTrial");
+#if defined(OS_LINUX) || defined(OS_CHROMEOS)
+  // TODO(gavinp): Remove this experiment in the m53 timeframe.
+  if (experiment_name == "ExperimentNo" ||
+      experiment_name == "ExperimentControl") {

[Alexei Svitkine (slow), 2016/05/13 18:40:51]

If enabled is the new behavior, then any experiment that changes this should
have control group specify the new behavior.

Also, suggests changing the check to StartsWith() per our best practices. You
can also change the one below to be StartsWith() "ExperimentYes" to avoid
needing the two =='s.

[gavinp, 2016/05/13 19:03:39]

Good point. I've renamed the group "Disable" for the new world with Simple Cache
everywhere.
Done.

+    return net::CACHE_BACKEND_BLOCKFILE;
+  }
+  return net::CACHE_BACKEND_SIMPLE;
+#else
   if (experiment_name == "ExperimentYes" ||
       experiment_name == "ExperimentYes2") {
     return net::CACHE_BACKEND_SIMPLE;
   }
   return net::CACHE_BACKEND_BLOCKFILE;
-#endif
+#endif  // #if defined(OS_LINUX) || defined(OS_CHROMEOS)
+#endif  // #if defined(OS_ANDROID)
 }
 
 }  // namespace
 
 using content::BrowserThread;
 
 ProfileImplIOData::Handle::Handle(Profile* profile)
     : io_data_(new ProfileImplIOData),
       profile_(profile),
       initialized_(false) {
@@ skipping 675 matching lines @@
     const base::Closure& completion) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   DCHECK(initialized());
 
   DCHECK(transport_security_state());
   // Completes synchronously.
   transport_security_state()->DeleteAllDynamicDataSince(time);
   DCHECK(http_server_properties_manager_);
   http_server_properties_manager_->Clear(completion);
 }