Bug 1442155 Fix extension names in Android install prompts r=johannh

This is pretty short and sweet since everything goes through
_prepareStrings and in bug 1431242 Prathiksha standardized our
handling of the "header" string.

MozReview-Commit-ID: 6t1kWmxVoyt

--HG--
extra : rebase_source : 55227dd71cb089ab4759fc145a02f65d131faa22

mobile/android/chrome/content/ExtensionPermissions.js

@@ -21,7 +21,7 @@ var ExtensionPermissions = {
     }
 
     return {
-      header: strings.header || strings.text,
+      header: strings.header.replace("<>", info.addonName),
       message,
       acceptText: strings.acceptText,
       cancelText: strings.cancelText,