Virtual scroll infinite loop in both direction

Bug, feature request, or proposal:

Feature request

What is the expected behavior?

Infinite scroll in both direction

What is the current behavior?

Currently the infinite scroll is not possible in both direction

What is the use-case or motivation for changing an existing behavior?

I am using horizontal virtual scroll, I need to provide infinite scroll in both direction and keep the current index always in center of the view port

Assume the array is

[0][1][2][3][4][5][6][7][8][9]

                       currIndex
                          |       
  [6][7]       |   [8][9][0][1][2]   |   [3][4][5]
Not rendered   |      Rendered       |  Not rendered

Let’s say user go to viewport.scrollToIndex(2)

                       currIndex
                          |       
  [8][9]       |   [0][1][2][3][4]   |   [5][6][7]
Not rendered   |      Rendered       |  Not rendered

Which versions of Angular, Material, OS, TypeScript, browsers are affected?

Angular: 7.0.1 Material: 7.0.2

Is there anything else we should know?

[mmalerba]

here’s an example that adds new copies of the data when you get near the end of the list: https://stackblitz.com/edit/angular-qpsjxm?file=app/cdk-virtual-scroll-data-source-example.ts

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