Add --enable-panels flag to about:flags.

chrome/app/generated_resources.grd

Index: chrome/app/generated_resources.grd
diff --git a/chrome/app/generated_resources.grd b/chrome/app/generated_resources.grd
index 94b007e25ce75b670a398a3ec5bf543cd6b74a62..e13e00e6d0b33cee2eaae3e8f6e64f2df5cf481a 100644
--- a/chrome/app/generated_resources.grd
+++ b/chrome/app/generated_resources.grd
@@ -4376,6 +4376,13 @@ Keep your key file in a safe place. You will need it to create new versions of y
       <message name="IDS_FLAGS_ENABLE_ADDITIONAL_AUTOFILL_FEEDBACK_DESCRIPTION" desc="Description for the flag to enable prompts for Autofill feedback">
         Help improve Autofill.  With this enabled, Chrome will occasionally prompt you to send additional feedback to the Autofill team.
       </message>
+      <message name="IDS_FLAGS_ENABLE_PANELS_NAME" desc="Name of the 'Enable Pane
+ls' lab.">
+        Panels
+      </message>
+      <message name="IDS_FLAGS_ENABLE_PANELS_DESCRIPTION" desc="Description for the flag to enable Panel windows.">
+        Enable experimental extensions to open Panel windows outside of the browser frame.
+      </message>
 
       <!-- Crashes -->
       <message name="IDS_CRASHES_TITLE" desc="Title for the chrome://crashes page.">