md-slider: when scrolling to see a slider, the dragging event is caught above the slider

[dorduchovni]

steps to reproduce:

1. go to codepan
2. scroll down the screen to see the sliders
3. try to drag any slider.

(reproduction gif)

[ThomasBurleson]

Will not fix.

[avivr]

Hey @ThomasBurleson,

Can you please explain why this issue won't be fixed?

We've also tried to use the new vertical mdSlider introduced in version 1.1.0-rc1,
and we see the same behaviour described in the bug.

The vertical slider is practically unusable in pages with scrollbar.

Tested with Chrome v50 both on Mac and Windows 10.

This looks like a duplicate of issue #7569 (which has PR #7617).

Thanks!
Aviv