Add simple cache backend experiment hidden behind a flag.

chrome/browser/chrome_browser_field_trials.cc

Index: chrome/browser/chrome_browser_field_trials.cc
diff --git a/chrome/browser/chrome_browser_field_trials.cc b/chrome/browser/chrome_browser_field_trials.cc
index 1c9a854e5c034f3c4c1a199cb271b27e3dab09aa..904d5ab594baf873ed313c00903c98961c94b3d1 100644
--- a/chrome/browser/chrome_browser_field_trials.cc
+++ b/chrome/browser/chrome_browser_field_trials.cc
@@ -59,6 +59,7 @@ ChromeBrowserFieldTrials::~ChromeBrowserFieldTrials() {
 void ChromeBrowserFieldTrials::SetupFieldTrials(
     const base::Time& install_time) {
   chrome_variations::SetupUniformityFieldTrials(install_time);
+  SetUpSimpleCacheFieldTrial();

[SteveT, 2013/03/15 14:07:05]

We might want to wrap this in a SetupAndroidFieldTrials method which can be set
to only compile on Android.

[pasko-google - do not use, 2013/03/15 15:36:28]

That makes sense in general. Right now we want it be available on all platforms
for ease of development. Hidden behind a flag.

Later we will switch the experiment to live on Android and probably iOS too. And
I did not find yet where the code for controlling iOS experiments should be
living.

 #if !defined(OS_ANDROID)
   SetupDesktopFieldTrials();
 #endif  // defined(OS_ANDROID)
@@ -191,6 +192,18 @@ void ChromeBrowserFieldTrials::DisableShowProfileSwitcherTrialIfNecessary() {
   }
 }
 
+void ChromeBrowserFieldTrials::SetUpSimpleCacheFieldTrial() {
+  if (parsed_command_line_.HasSwitch(switches::kUseSimpleCacheBackend)) {

[SteveT, 2013/03/15 14:07:05]

You want the user to turn on the switch in order to even consider rolling the
dice for the experiment?

[pasko-google - do not use, 2013/03/15 15:36:28]

Yes. This will change when we tune the experiment parameters. I outlined this in
the header file.

+    const base::FieldTrial::Probability kDivisor = 100;
+    base::FieldTrial::Probability simple_cache_probability = 100;
+    scoped_refptr<base::FieldTrial> trial(
+        base::FieldTrialList::FactoryGetFieldTrial("SimpleCacheTrial", kDivisor,
+                                                   "No", 2013, 12, 31, NULL));
+    trial->UseOneTimeRandomization();
+    trial->AppendGroup("Yes", simple_cache_probability);

[SteveT, 2013/03/15 14:07:05]

This sets up the trial so that everyone gets the "Yes" group. Is this what you
meant to do? If so, why?

Your CL description seems to imply that this is temporary and later you'll be
making changes to get the true flag behaviour.

[pasko-google - do not use, 2013/03/15 15:36:28]

Yes, exactly. It is the way to enable a 100% experiment with the flag. For
development period only.

+  }
+}
+
 void ChromeBrowserFieldTrials::SetUpCacheSensitivityAnalysisFieldTrial() {
   const base::FieldTrial::Probability kDivisor = 100;