Bug 598923 - add-on bar should be made visible if there are any add-ons installed (r=dao, a=blocking)

browser/base/content/browser.js

@@ -1378,6 +1378,7 @@ function delayedStartup(isLoadingBlank, mustLoadSidebar) {
   OfflineApps.init();
   IndexedDBPromptHelper.init();
   gFormSubmitObserver.init();
+  AddonManager.addAddonListener(AddonsMgrListener);
 
   gBrowser.addEventListener("pageshow", function(evt) { setTimeout(pageShowEventHandlers, 0, evt); }, true);
 
@@ -1641,6 +1642,7 @@ function BrowserShutdown()
   OfflineApps.uninit();
   gPrivateBrowsingUI.uninit();
   IndexedDBPromptHelper.uninit();
+  AddonManager.removeAddonListener(AddonsMgrListener);
 
   var enumerator = Services.wm.getEnumerator(null);
   enumerator.getNext();
@@ -8050,3 +8052,33 @@ function duplicateTabIn(aTab, where, historyIndex) {
       break;
   }
 }
+
+/*
+ * When addons are installed/uninstalled, check and see if the number of items
+ * on the add-on bar changed:
+ * - If an add-on was installed, incrementing the count, show the bar.
+ * - If an add-on was uninstalled, and no more items are left, hide the bar.
+ */
+let AddonsMgrListener = {
+  get addonBar() document.getElementById("addon-bar"),
+  get statusBar() document.getElementById("status-bar"),
+  getAddonBarItemCount: function() {
+    // Take into account the contents of the status bar shim for the count.
+    return this.addonBar.childNodes.length - 1 +
+           this.statusBar.childNodes.length;
+  },
+  onInstalling: function(aAddon) {
+    this.lastAddonBarCount = this.getAddonBarItemCount();
+  },
+  onInstalled: function(aAddon) {
+    if (this.getAddonBarItemCount() > this.lastAddonBarCount)
+      setToolbarVisibility(this.addonBar, true);
+  },
+  onUninstalling: function(aAddon) {
+    this.lastAddonBarCount = this.getAddonBarItemCount();
+  },
+  onUninstalled: function(aAddon) {
+    if (this.lastAddonBarCount > 0 && this.getAddonBarItemCount() == 0)
+      setToolbarVisibility(this.addonBar, false);
+  }
+};

browser/base/content/test/Makefile.in

@@ -160,6 +160,7 @@ _BROWSER_FILES = \
                  browser_bug595507.js \
                  browser_bug596687.js \
                  browser_bug597218.js \
+                 browser_bug598923.js \
                  browser_bug599325.js \
                  browser_bug609700.js \
                  browser_contextSearchTabPosition.js \

browser/base/content/test/browser_bug598923.js

@@ -0,0 +1,32 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+// Test:
+// * if add-on is installed to the add-on bar, the bar is made visible.
+// * if add-on is uninstalled from the add-on bar, and no more add-ons there,
+//   the bar is hidden.
+
+function test() {
+  let aml = AddonsMgrListener;
+  ok(aml, "AddonsMgrListener exists");
+  // check is hidden
+  is(aml.addonBar.collapsed, true, "aob is hidden");
+  // aob gets the count
+  AddonsMgrListener.onInstalling();
+  // add an item
+  let element = document.createElement("toolbaritem");
+  aml.addonBar.appendChild(element);
+  // aob checks the count, makes visible
+  AddonsMgrListener.onInstalled();
+  // check is visible
+  is(aml.addonBar.collapsed, false, "aob is visible");
+  // aob gets the count
+  AddonsMgrListener.onUninstalling();
+  // remove an item
+  aml.addonBar.removeChild(element);
+  // aob checks the count, makes hidden
+  AddonsMgrListener.onUninstalled();
+  // check is hidden
+  is(aml.addonBar.collapsed, true, "aob is hidden");
+}