fix(tabs): ie10 MutationObserver issue

[j3ski]

Check if MutationObserver is in window. If not fall back to DOMSubtreeModified event.

Closes: 9395

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[j3ski]

I signed it!

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[crisbeto]

@j3ski I haven't tried this out yet, but I believe that DOMSubtreeModified is deprecated and fires very often. It might be a good idea to see if this can either be switched to an Angular watcher that "only" fires once per digest, or look into debouncing the callback (You can use the $mdUtil.debounce method).

[j3ski]

@crisbeto Yes, DOMSubtreeModified is deprecated, but this is a fix for browsers which don't yet support MutationObserver. I re-implemented the functionality removed here. I don't think this can be switched to an Angular watcher, as the MutationObserver watches for subtree modifications, not attributes, but debouncing sounds like a good idea. Initially the DOMSubtreeModified would fire up to 9x more often than MutationObserver in my case. Debounced it fires roughly the same amount of times as MutationObserver (provided MO did fire), however it fires on more occasions.

[crisbeto]

This looks good, although could you change the debounce signature to $mdUtil.debounce(mutationCallback, 15, null, false)? This is because a couple of reasons:

1. Passing in false as the last param means that it won't trigger a digest every time it gets invoked, which should help with the performance.
2. Bumping the time is more of a nitpick, but I feel that it's something we can get away with since it's still less than 1 frame (which is ~16ms).

[j3ski]

Done.
Checked it, reduced the number of calls to mutationCallback by 1 in one scenario. Also the app seems to work smoother when loading the tabs, but it can be just my impression.

[crisbeto]

Great, I'll test it out manually a bit later.

[crisbeto]

Code and functionality-wise LGTM @ThomasBurleson. The commits should be squashed though.