Bug 1414838 - Show stop button again as soon as page loading starts. r=nechen

As of bug 1366672, case START no longer falls through in order to allow for a
different behaviour of the progress indicator, however we still need to add
UpdateFlags.PROGRESS, so that the stop button shows up as soon as a page starts
loading.

MozReview-Commit-ID: 3P33JEsS5ic

--HG--
extra : rebase_source : 4f83ab57613df31cdd4f392c478df33a992c95af

mobile/android/base/java/org/mozilla/gecko/toolbar/BrowserToolbar.java

@@ -464,6 +464,7 @@ public abstract class BrowserToolbar extends ThemedRelativeLayout
             // Progress-related handling
             switch (msg) {
                 case START:
+                    flags.add(UpdateFlags.PROGRESS);
                     updateProgressVisibility(tab, Tab.LOAD_PROGRESS_INIT);
                     break;
                 case ADDED: