Bug 830404 - Re-insert accidently removed string. r=mfinkle

mobile/android/locales/en-US/chrome/aboutDownloads.properties

@@ -7,6 +7,8 @@
 # http://developer.mozilla.org/en/docs/Localization_and_Plurals
 downloadMessage.deleteAll=Delete this download?;Delete #1 downloads?
 
+downloadAction.deleteAll=Delete All
+
 downloadState.downloading=Downloading…
 downloadState.canceled=Canceled
 downloadState.failed=Failed