feat(ngMock) add atomic flushing strategy for $timeout

[elkeis]

Hi dear angular community,

During writing unit-tests I found one interesting issue. I need to write tests for some code like this:

$timeout(function() {
 action1();
 $timeout(function() {
  action2();
 });
});

And I'm expecting that i need to execute $timeout.flush() 2 times. First time to reach action1 function and the second time to execute action2 function (let's call this kind of flush "atomic" for example). But for now, for the first flush() it executes the both handlers. One after another. Please check this example: http://jsbin.com/fuziri/edit?js,output .

At the other hand we have some cases in tests when this buggy, for the first look, behaviour can simplify our lifes. In such case for example:

 var callback = jasmine.createSpy();
 $timeout(function() {}, 0, false).then(callback);
 $timeout.flush();
 expect(callback).toHaveBeenCalled();

Here $timeout register new defered task to process callback using $browser.defer during flushing. So to execute callback (if you are using that atomic flush strategy) you should call $timeout.flush() twise.

I think that the both strategies of flushing are pretty useful. And may be it will be a good idea to allow to switch between them, using some additional parameter.

I implemented solution which works for me. What do you think about this?

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