New post-sideload UI:

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 8e31cde202d500a372450cb496f3eb603c19e8bf..1539a3e270db23206c3fb58a2b81f93e75c92f2a 100644
--- a/chrome/app/generated_resources.grd
+++ b/chrome/app/generated_resources.grd
@@ -5304,7 +5304,7 @@ Keep your key file in a safe place. You will need it to create new versions of y
       </message>
 
       <!-- Global error messages for extensions -->
-      <message name="IDS_EXTENSION_WARNINGS_WRENCH_MENU_ITEM" desc="The wrench menu item indicating that extensions caused problems">
+      <message name="IDS_EXTENSION_WARNINGS_WRENCH_MENU_ITEM" desc="The wrench menu item indicating that extensions caused problems.">
         Extension error
       </message>
       <message name="IDS_EXTENSION_WARNINGS_TITLE" desc="The title of a section in chrome://extensions which contains the warning(s) that relates to one particular extension">
@@ -5317,6 +5317,29 @@ Keep your key file in a safe place. You will need it to create new versions of y
         This extension failed to modify a network request because the modification conflicted with another extension.
       </message>
 
+      <!-- External extension install alerts -->
+      <!-- TODO(mpcomplete): We may need to change Chrome to
+           PRODUCT_NAME. Leaving it as-is until we finalize
+           these strings. -->
+      <message name="IDS_EXTENSION_EXTERNAL_INSTALL_ALERT" desc="The wrench menu item indicating that a new external extension was installed.">
+        New extension added (<ph name="EXTENSION_NAME">$1<ex>Babylon Toolbar</ex></ph>)

[Jeffrey Yasskin, 2012/10/13 21:17:35]

It would be nice to present a count instead of a single name if multiple
extensions were installed.

[Matt Perry, 2012/10/15 19:13:38]

That should be a pretty occurrence. When it does happen, we just queue them up
and show them one at a time.

[Yoyo Zhou, 2012/10/16 23:28:05]

If this is 

+      </message>
+      <message name="IDS_EXTENSION_EXTERNAL_INSTALL_PROMPT_TITLE" desc="">
+        "<ph name="EXTENSION_NAME">$1<ex>Babylon Toolbar</ex></ph>" added
+      </message>
+      <message name="IDS_EXTENSION_EXTERNAL_INSTALL_PROMPT_HEADING" desc="">
+        While you were out, another program on your computer added an extension to Chrome.
+      </message>
+      <message name="IDS_EXTENSION_EXTERNAL_INSTALL_PROMPT_MAY_CHANGE_CHROME" desc="">
+        This extension may change the way Chrome works.
+      </message>
+      <message name="IDS_EXTENSION_EXTERNAL_INSTALL_PROMPT_ACCEPT_BUTTON" desc="">
+        Enable extension
+      </message>
+      <message name="IDS_EXTENSION_EXTERNAL_INSTALL_PROMPT_ABORT_BUTTON" desc="">
+        Remove from Chrome
+      </message>
+
       <!-- Plugins -->
       <message name="IDS_PLUGINS_TITLE" desc="Title for the chrome://plugins page.">
         Plug-ins