Bug 1297117 - Add documentation to stripAboutReaderUrl r=sebastian

MozReview-Commit-ID: Ibzhnk7LLmh

--HG--
extra : histedit_source : f8460143a4c00238defb68774e96ac99150779aa

mobile/android/base/java/org/mozilla/gecko/reader/ReaderModeUtils.java

@@ -45,6 +45,12 @@ public class ReaderModeUtils {
         return getAboutReaderForUrl(url, -1);
     }
 
+    /**
+     * Obtain the underlying URL from an about:reader URL.
+     * This will return the input URL if either of the following is true:
+     * 1. the input URL is a non about:reader URL
+     * 2. the input URL is an invalid/unparseable about:reader URL
+     */
     public static String stripAboutReaderUrl(String url) {
         if (!AboutPages.isAboutReader(url)) {
             return url;