Fix timers after suspend/resume/pause

We use timers to decide when to query and delete expired messages or
when to perform signed key rotations.

Internally, timers are counters that get updated when the CPU ticks, so
if the CPU sleeps, the timer will stop counting, and start again after
it wakes up, ignoring the intervening passage of wall clock time.

To fix this, without having to query the database or other potentially
high overhead operations too often, use an interval to frequently check
the wall clock time. If time jumps forward, trigger a global event so
other listeners can update their possibly-inaccurate timers.

https://stackoverflow.com/questions/6346849/what-happens-to-settimeout-when-the-computer-goes-to-sleep
https://stackoverflow.com/questions/4079115/can-any-desktop-browsers-detect-when-the-computer-resumes-from-sleep

// FREEBIE

background.html

@@ -541,6 +541,7 @@
   <script type='text/javascript' src='js/views/identicon_svg_view.js'></script>
   <script type='text/javascript' src='js/views/settings_view.js'></script>
 
+  <script type='text/javascript' src='js/wall_clock_listener.js'></script>
   <script type='text/javascript' src='js/rotate_signed_prekey_listener.js'></script>
   <script type='text/javascript' src='js/background.js'></script>
 </head>

js/background.js

@@ -87,8 +87,9 @@
             openInbox();
         }
 
+        WallClockListener.init();
         RotateSignedPreKeyListener.init();
-        ExpiringMessagesListener.update();
+        ExpiringMessagesListener.init();
     });
 
     window.getSyncRequest = function() {

js/expiring_messages.js

@@ -37,6 +37,10 @@
     }
 
     window.ExpiringMessagesListener = {
+        init: function() {
+            checkExpiringMessages();
+            window.events.on('timetravel', checkExpiringMessages);
+        },
         update: checkExpiringMessages
     };
 

js/rotate_signed_prekey_listener.js

@@ -53,6 +53,11 @@
                 scheduleNextRotation();
                 setTimeoutForNextRun();
             });
+            window.events.on('timetravel', function() {
+                if (Whisper.Registration.isDone()) {
+                    setTimeoutForNextRun();
+                }
+            });
         }
     };
 }());

js/wall_clock_listener.js

@@ -0,0 +1,25 @@
+/*
+ * vim: ts=4:sw=4:expandtab
+ */
+
+;(function () {
+    'use strict';
+
+    var lastTime;
+    var interval = 1000;
+    function checkTime() {
+      var currentTime = Date.now();
+      if (currentTime > (lastTime + interval * 2)) {
+          console.log('time travel detected!');
+          window.events.trigger('timetravel');
+      }
+      lastTime = currentTime;
+    }
+
+    window.WallClockListener = {
+      init: function() {
+          lastTime = Date.now();
+          setInterval(checkTime, 1000);
+      }
+    };
+}());