fix(mocks): $timeout#flush should not update time when empty

When $timeout#flush is called with a delay and no task can be flushed within that
delay, the current time should not be updated as that gets the mock into an inconsistent
state.

BREAKING CHANGE: if a tests was written around the buggy behavior the delays might be off now

This would typically not be a problem, but because of the previous breaking change in
$timeout.flush, the combination of two might be confusing and that's why we are documenting
it.

Old behavior:

```
doSomething(); //schedules task to execute in 500ms from now
doOtherStuff(); //schedules task to execute in 600ms from now

try {
  $timeout.flush(300); // throws "no task to be flushed" exception
} catch(e) {};
$time.flush(200); //flushes only doSomething() task
```

New behavior:

```
doSomething(); //schedules task to execute in 500ms from now
doOtherStuff(); //schedules task to execute in 600ms from now

try {
  $timeout.flush(300); // throws "no task to be flushed" exception
} catch(e) {};
$time.flush(200); // throws "no task to be flushed" exception again
                  // because previous exception didn't move the time forward
```

Fixed test:

```
doSomething(); //schedules task to execute in 500ms from now
doOtherStuff(); //schedules task to execute in 600ms from now

try {
  $timeout.flush(300); // throws "no task to be flushed" exception
} catch(e) {};
$time.flush(500); // flushes only doSomething() task
```

1 files changed, 6 insertions, 3 deletions

diff --git a/src/ngMock/angular-mocks.js b/src/ngMock/angular-mocks.js
index 05fdc4ed..d0c1b9b2 100644
--- a/src/ngMock/angular-mocks.js
+++ b/src/ngMock/angular-mocks.js
@@ -105,16 +105,17 @@ angular.mock.$Browser = function() {
    */
   self.defer.flush = function(delay) {
     var flushedSomething = false;
+        now = self.defer.now;
 
     if (angular.isDefined(delay)) {
-      self.defer.now += delay;
+      now += delay;
     } else {
       if (self.deferredFns.length) {
-        self.defer.now = self.deferredFns[self.deferredFns.length-1].time;
+        now = self.deferredFns[self.deferredFns.length-1].time;
       }
     }
 
-    while (self.deferredFns.length && self.deferredFns[0].time <= self.defer.now) {
+    while (self.deferredFns.length && self.deferredFns[0].time <= now) {
       flushedSomething = true;
       self.deferredFns.shift().fn();
     }
@@ -126,6 +127,8 @@ angular.mock.$Browser = function() {
         throw Error('No deferred tasks with delay up to ' + delay + 'ms to be flushed!')
       }
     }
+
+    self.defer.now = now;
   };
 
   /**