Add e2e tests for $anchorScroll

[gkalpak]

It would make sense to have some e2e tests for $anchorScroll in order to test the actual scrolling (especially in regard to the yOffset functonality - once #9517 lands).

Since putting these in the docs app is a little too much, we should add the tests as soon as #9527 gets implemented.

/ping @petebacondarwin , @tbosch

[gkalpak]

In the meantime I have added some e2e tests in the docs app (#9583).
There still is functionality that needs to be tested, but it's a start.

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My concern is whether the tests' complexity might scare people away !
Either because one has to interact with the window and the DOM (via async lower-level WebDriver APIs) or because I am missing a more straightforward way to write them, the tests look quite more complex that "usual" protractor tests.
Insights welcome :)

/cc @petebacondarwin

[tbosch]

Note: The syntax for this tests could be made simpler if we added some helper methods and matchers for testing animations in general (e.g. expect a movement from a to b, ...).