fix(ngAnimate): do not use event.timeStamp anymore for time tracking

[matsko]

Due to recent changes in Chrome, Firefox and Webkit use of the
event.timeStamp value will lead to unpredictable behaviour due to
precision changes. Therefore it's best to stick entirely to use
Date.now() when it comes to confirming the end of transition-
ending values. See #13494 for more info.

Applies to 1.2, 1.3, 1.4 and 1.5.

Closes #13494

[petebacondarwin]

LGTM

[majido]

It may actually be best to use performance.now() instead of Date.now(). That provides a more accurate time and more importantly perhaps it is not subject to systems time skews making it more appropriate to measure time periods such as this. That means a bit more work to to change the startTime and perhaps some of your tests.

[petebacondarwin]

@majido - Although since Performance.now() is not available on all the platforms we support, we would have to have a fallback to Date.now() anyway.

[Narretz]

The only browser who doesn't support it is IE9 (obviously). But we can still switch to performance.now later.

[petebacondarwin]

Let's go with Date.now() for the moment and reconsider Performance.now() if issues appear.