Reland fast tab closure behind a flag

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 a06629c60099bc8d067ca806baefbb72582343f3..ffdc5cb2d098917e094547b72d18d4a02454a50c 100644
--- a/chrome/app/generated_resources.grd
+++ b/chrome/app/generated_resources.grd
@@ -6440,6 +6440,12 @@ Keep your key file in a safe place. You will need it to create new versions of y
       <message name="IDS_FLAGS_EXTENSIONS_ON_CHROME_URLS_DESCRIPTION" desc="Description of the 'Extensions on chrome:// URLs' lab">
         Enables running extensions on chrome:// URLs, where extensions explicitly request this permission.
       </message>
+      <message name="IDS_FLAGS_ENABLE_FAST_UNLOAD_DESCRIPTION" desc="Description of the 'Fast Unload' lab.">
+        Enables fast tab/window closing - runs a tab's onunload js handler independently of the GUI.
+      </message>
+      <message name="IDS_FLAGS_ENABLE_FAST_UNLOAD_NAME" desc="Name of the 'Extensions on chrome:// URLs' lab">
+        Enable fast tab/window close
+      </message>
       <message name="IDS_FLAGS_ENABLE_ADVIEW_NAME" desc="Name of the 'Enable 'adview' element' lab.">
         Enable 'adview' element
       </message>