No browserless Panels unless enabled by flag.

chrome/browser/ui/panels/panel_manager.cc

Index: chrome/browser/ui/panels/panel_manager.cc
diff --git a/chrome/browser/ui/panels/panel_manager.cc b/chrome/browser/ui/panels/panel_manager.cc
index 10bf8ca84798f76c0a28ac5bde66d427a64b3ebe..9f50e8ee228ce1093e002477a1d9ae852c2ed512 100644
--- a/chrome/browser/ui/panels/panel_manager.cc
+++ b/chrome/browser/ui/panels/panel_manager.cc
@@ -93,8 +93,14 @@ bool PanelManager::UseBrowserlessPanels() {
   if (CommandLine::ForCurrentProcess()->HasSwitch(switches::kOldPanels))
     return false;
 
-  return chrome::VersionInfo::GetChannel() <=
-      chrome::VersionInfo::CHANNEL_UNKNOWN;
+  // http://crbug.com/143506
+  // TODO(jennb): Remove after channel check can be used.
+// return chrome::VersionInfo::GetChannel() <= chrome::VersionInfo::CHANNEL_DEV;
+  // For now, use former flag to turn on browserless panels.
+  if (CommandLine::ForCurrentProcess()->HasSwitch(switches::kBrowserlessPanels))
+    return true;
+
+  return false;
 }
 
 PanelManager::PanelManager()