feat(material-experimental): add test harness for slider

[devversion]

No description provided.

[devversion]

@jelbourn @mmalerba I wasn't too sure how we can solve the setValue thing. There are two options:

1. Setting the value through click (this is what currently is implemented as part of 51e4daa)
   • Can deviate in rare cases since not each value maps to a single pixel (that we an click).
2. Setting the value by pressing the up or down arrow keys. This is unpredictable since the keys always cause a change based on the specified mat-slider#step.
   • Developer could specify a value that can't be selected through keyboard but got set through binding for example.

If we want to spend some more time exploring the options, I'd propose that we do this as a follow-up. That's why the logic for setting a value is in a separate commit.

[mmalerba]

Ah that's interesting... I guess a real user would have similar difficulty using your slider if you didn't have it set so that all values can be reached via the keyboard or had more steps than pixels worth of track.

I guess I would say go for the clicking approach like you've done and maybe document that if you have more steps than pixels the setValue could be slightly off, but also that it would be a bad experience for your users and you should change it

[devversion]

@mmalerba Done. I'm wondering if we should consider providing a method for selecting a value through keyboard interaction too. The arrow keys allow granular control over the value since those allow changes by "one step value" but in order to provide meaningful methods.. we'd need to somehow determine the step value from within the harness (which requires some host bindings on the slider..). I think that's something we could explore in a follow-up PR.

[jelbourn]

I also agree that methods to increment/decrement by the step via keyboard would be good in a follow-up.

[devversion]

@jelbourn @mmalerba Addressed feedback.

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