Field trials are currently implemented (commonly) using a static variable that is set

once, the first time it is necessary to decide if there is an experiment by a given 
name active.

With this change the field-test system can "push" a group that is selected for 
the given field trial (field test) if/when an experiment does arrive.

This change implements a simple IPC notification of the result of a FieldTrial
setting being sent to any previously started renderers.

BUG=16494
TEST=field trial tests
R=jar
Review URL: http://codereview.chromium.org/6883029

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@83488 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 52 insertions, 0 deletions

diff --git a/chrome/browser/metrics/field_trial_synchronizer.cc b/chrome/browser/metrics/field_trial_synchronizer.cc
new file mode 100644
index 0000000..0e7484f
--- /dev/null
+++ b/chrome/browser/metrics/field_trial_synchronizer.cc
@@ -0,0 +1,52 @@
+// Copyright (c) 2011 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/metrics/field_trial_synchronizer.h"
+
+#include "base/logging.h"
+#include "base/threading/thread.h"
+#include "chrome/common/chrome_constants.h"
+#include "chrome/common/render_messages.h"
+#include "content/browser/browser_thread.h"
+#include "content/browser/renderer_host/render_process_host.h"
+
+FieldTrialSynchronizer::FieldTrialSynchronizer() {
+  DCHECK(field_trial_synchronizer_ == NULL);
+  field_trial_synchronizer_ = this;
+  base::FieldTrialList::AddObserver(this);
+}
+
+FieldTrialSynchronizer::~FieldTrialSynchronizer() {
+  base::FieldTrialList::RemoveObserver(this);
+  field_trial_synchronizer_ = NULL;
+}
+
+void FieldTrialSynchronizer::NotifyAllRenderers(
+    const std::string& field_trial_name,
+    const std::string& group_name) {
+  // To iterate over RenderProcessHosts, or to send messages to the hosts, we
+  // need to be on the UI thread.
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+
+  for (RenderProcessHost::iterator it(RenderProcessHost::AllHostsIterator());
+       !it.IsAtEnd(); it.Advance()) {
+    it.GetCurrentValue()->Send(
+        new ViewMsg_SetFieldTrialGroup(field_trial_name, group_name));
+  }
+}
+
+void FieldTrialSynchronizer::OnFieldTrialGroupFinalized(
+    const std::string& field_trial_name,
+    const std::string& group_name) {
+  BrowserThread::PostTask(
+      BrowserThread::UI, FROM_HERE,
+      NewRunnableMethod(this,
+                        &FieldTrialSynchronizer::NotifyAllRenderers,
+                        field_trial_name,
+                        group_name));
+}
+
+// static
+FieldTrialSynchronizer*
+    FieldTrialSynchronizer::field_trial_synchronizer_ = NULL;