New post-sideload UI:

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 4b600e20fcfedca48b11da36bda09bc2e3f73e7c..e826b0c0f5b12265a506da44f2ce00f19d7df2ab 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -696,6 +696,10 @@ const char kExtensionsUpdateFrequency[]     = "extensions-update-frequency";
 // Should we use an external Autofill popup?  Default is no.
 const char kExternalAutofillPopup[]         = "external-autofill-popup";
 
+// Should we prompt the user before allowing external extensions to install?
+// Default is yes.
+const char kExternalExtensionPrompt[]       = "external-extension-prompt";
+
 // These two flags are added around the switches about:flags adds to the
 // command line. This is useful to see which switches were added by about:flags
 // on about:version. They don't have any effect.