Bug 739866 - Store last accessed timestamp for tabbrowser tabs [r=zpao]

browser/base/content/tabbrowser.xml

@@ -924,6 +924,7 @@
 
             if (!this._previewMode) {
               this.mCurrentTab.removeAttribute("unread");
+              this.selectedTab.lastAccessed = Date.now();
 
 #ifdef MOZ_E10S_COMPAT
               // Bug 666816 - TypeAheadFind support for e10s
@@ -3816,6 +3817,7 @@
       <field name="mCorrespondingMenuitem">null</field>
       <field name="_fullyOpen">false</field>
       <field name="closing">false</field>
+      <field name="lastAccessed">0</field>
     </implementation>
 
     <handlers>

browser/base/content/test/Makefile.in

@@ -273,6 +273,7 @@ _BROWSER_FILES = \
                  browser_middleMouse_inherit.js \
                  redirect_bug623155.sjs \
                  browser_tabDrop.js \
+                 browser_lastAccessedTab.js \
                  $(NULL)
 
 ifneq (cocoa,$(MOZ_WIDGET_TOOLKIT))

browser/base/content/test/browser_lastAccessedTab.js

@@ -0,0 +1,24 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+/**
+ * Test for bug 739866.
+ *
+ * 1. Adds a new tab (but doesn't select it)
+ * 2. Checks if timestamp on the new tab is 0
+ * 3. Selects the new tab, checks that the timestamp is updated (>0)
+ * 4. Selects the original tab & checks if new tab's timestamp has remained changed
+ */
+
+function test() {
+  let originalTab = gBrowser.selectedTab;
+  let newTab = gBrowser.addTab("about:blank", {skipAnimation: true});
+  is(newTab.lastAccessed, 0, "Timestamp on the new tab is 0.");
+  gBrowser.selectedTab = newTab;
+  let newTabAccessedDate = newTab.lastAccessed;
+  ok(newTabAccessedDate > 0, "Timestamp on the selected tab is more than 0.");
+  ok(newTabAccessedDate <= Date.now(), "Timestamp less than or equal current Date.");
+  gBrowser.selectedTab = originalTab;
+  is(newTab.lastAccessed, newTabAccessedDate, "New tab's timestamp remains the same.");
+  gBrowser.removeTab(newTab);
+}