Facilitate a FieldTrial in the renderer

I added a command line for the renderer that accepts a FieldTrial
name and value, and forces that value to be activated in the
renderer.  As a result, any FieldTrial setting that is specified
by the browser process can be set (forced) in the renderer
process.  Such settings can then be used to establish names
of histograms, which means all processes can work in sync
on a single field trial (and generate data).  This should
allow A/B tests to be run that modulate the page load times.

Dave: Please review/confirm that you are happy with the changes to
render_view.cc.  Note that all I did was change the names and limits
for the histograms (they now go up to 3 minutes).  The MakeName()
allows me to get an A/B test of the impact of DNS pre-resolution.

Mike: Please review the code for passing along switch settings.

r=davemoore,mbelshe
Review URL: http://codereview.chromium.org/115525

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@16460 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 40 insertions, 0 deletions

diff --git a/base/field_trial.cc b/base/field_trial.cc
index d0085e6..fc12f31 100644
--- a/base/field_trial.cc
+++ b/base/field_trial.cc
@@ -13,6 +13,9 @@ using base::Time;
 // static
 const int FieldTrial::kNotParticipating = -1;
 
+// static
+const char FieldTrial::kPersistentStringSeparator('/');
+
 //------------------------------------------------------------------------------
 // FieldTrial methods and members.
 
@@ -50,6 +53,40 @@ std::string FieldTrial::MakeName(const std::string& name_prefix,
   return big_string.append(FieldTrialList::FindFullName(trial_name));
 }
 
+std::string FieldTrial::MakePersistentString() const {
+  DCHECK_EQ(name_.find(kPersistentStringSeparator), std::string::npos);
+  DCHECK_EQ(group_name_.find(kPersistentStringSeparator), std::string::npos);
+
+  std::string persistent(name_);
+  persistent = persistent.append(1, kPersistentStringSeparator);
+  persistent = persistent.append(group_name_);
+  return persistent;
+}
+
+// static
+FieldTrial* FieldTrial::RestorePersistentString(const std::string &persistent) {
+  size_t split_point = persistent.find(kPersistentStringSeparator);
+  if (std::string::npos == split_point)
+    return NULL;  // Bogus string.
+  std::string new_name(persistent, 0, split_point);
+  std::string new_group_name(persistent, split_point + 1);
+  if (new_name.empty() || new_group_name.empty())
+    return NULL;  // Incomplete string.
+
+  FieldTrial *field_trial;
+  field_trial = FieldTrialList::Find(new_name);
+  if (field_trial) {
+    // In single process mode, we may have already created the field trial.
+    if (field_trial->group_name_ != new_group_name)
+      return NULL;  // Conflicting group name :-(.
+  } else {
+    const int kTotalProbability = 100;
+    field_trial = new FieldTrial(new_name, kTotalProbability);
+    field_trial->AppendGroup(new_group_name, kTotalProbability);
+  }
+  return field_trial;
+}
+
 //------------------------------------------------------------------------------
 // FieldTrialList methods and members.
 
@@ -75,6 +112,9 @@ FieldTrialList::~FieldTrialList() {
 
 // static
 void FieldTrialList::Register(FieldTrial* trial) {
+  DCHECK(global_);
+  if (!global_)
+    return;
   AutoLock auto_lock(global_->lock_);
   DCHECK(!global_->PreLockedFind(trial->name()));
   trial->AddRef();