Add flag in about:flags page to enable / disable apps-devtool.

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 b1e84ef35d0a8638e33eee7e945b70897804be40..3654543afef7cf7420dda141e132d59ca06c4b6f 100644
--- a/chrome/app/generated_resources.grd
+++ b/chrome/app/generated_resources.grd
@@ -7140,6 +7140,12 @@ Keep your key file in a safe place. You will need it to create new versions of y
       <message name="IDS_FLAGS_ENABLE_SCREEN_CAPTURE_DESCRIPTION" desc="Description of flag to enable screen capture.">
         Allow web pages to request access to the screen contents via the getUserMedia() API.
       </message>
+      <message name="IDS_FLAGS_ENABLE_APPS_DEVTOOL_APP_NAME" desc="Name of the flag to enable apps-devtools app.">
+        Enable apps-devtool app.
+      </message>
+      <message name="IDS_FLAGS_ENABLE_APPS_DEVTOOL_APP_DESCRIPTION" desc="Description of flag to enable apps-devtools app.">
+        An app to develop apps / extensions.
+      </message>
 
       <!-- Crashes -->
       <message name="IDS_CRASHES_TITLE" desc="Title for the chrome://crashes page.">