No browserless Panels unless enabled by flag.

chrome/common/chrome_switches.cc

Index: chrome/common/chrome_switches.cc
diff --git a/chrome/common/chrome_switches.cc b/chrome/common/chrome_switches.cc
index 0acc4632826e1f62ded9c0f278607c082e2de27c..7218b010469188e8bffa0bcbed021acd55a22a33 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -129,6 +129,11 @@ const char kAutomationClientChannelID[]     = "automation-channel";
 const char kAutomationReinitializeOnChannelError[] =
     "automation-reinitialize-on-channel-error";
 
+// Use the (in-progress) refactor of desktop Panel windows which does not
+// require a Browser. Flag will be removed after refactor is ready to replace
+// existing BrowserWindow Panels.
+const char kBrowserlessPanels[] = "browserless-panels";
+
 // How often (in seconds) to check for updates. Should only be used for testing
 // purposes.
 const char kCheckForUpdateIntervalSec[]     = "check-for-update-interval";