Exclude extension settings strings for platforms that don't have extensions.

chrome/app/chromium_strings.grd

Index: chrome/app/chromium_strings.grd
diff --git a/chrome/app/chromium_strings.grd b/chrome/app/chromium_strings.grd
index ea24d1086182e3ba3640a703f07519090a36d1f0..96a31b3d01fba932a75797a146ac6581be505d99 100644
--- a/chrome/app/chromium_strings.grd
+++ b/chrome/app/chromium_strings.grd
@@ -771,9 +771,14 @@ For Chromium, processes used to display diagnostics information (such as this "a
       </message>
 
       <!-- Extension installed bubble -->
-      <message name="IDS_EXTENSION_INSTALLED_HEADING" desc="First line in the content area of the extension installed bubble. Instructs that the extension was installed.">
-        <ph name="EXTENSION_NAME">$1<ex>Gmail Checker</ex></ph> has been added to Chromium.
-      </message>
+      <if expr="enable_extensions">
+        <message name="IDS_EXTENSION_INSTALLED_HEADING" desc="First line in the content area of the extension installed bubble. Instructs that the extension was installed.">
+          <ph name="EXTENSION_NAME">$1<ex>Gmail Checker</ex></ph> has been added to Chromium.
+        </message>
+        <message name="IDS_EXTENSION_INSTALLED_SIGNIN_PROMO_LINK" desc="The first part of the sign-in promo paragraph. This part will be converted to a link and will get more text appended to it (see IDS_EXTENSION_INSTALLED_SIGNIN_PROMO). Keep this text short.">
+          Sign in to Chromium
+        </message>
+      </if>
 
       <!-- chrome://settings/extensions page -->
       <message name="IDS_EXTENSIONS_INCOGNITO_WARNING" desc="Warns the user that Chromium cannot prevent extensions from recording history in incognito mode. Displayed in extensions management UI after an extension is selected to be run in incognito mode.">