fix(cdk/overlay): fix wrong overflow calculation

[Goobles]

overflowBottom is currently calculated with viewport.bottom (which could be any number from the height of the viewport to as large as your page is)
calculating the overflow should just be difference between overlay.height + start.y and the height of the viewport, not the height of the entire page.

Right now the overlay is pushed out of the view in certain cases.

[jelbourn]

@Goobles can you create a stackblitz that shows the issue this is fixing? The part I don't follow here is that the overlayPoint and the viewportRect's right/bottom should be in the same coordinate space, so my understanding would be that bottom and right would be what we want since they include the scroll position of the page, while width and height don't.

[Goobles]

@jelbourn Here is a minimal reproduction of the bug I am experiencing:
https://stackblitz.com/edit/angular-payabe

[Goobles]

start.x and start.y are in the coordinate space of the overlay container, it does not contain the scrollposition of the page.

[jelbourn]

Thanks! I see now; the change looks good to me, then. The unit tests just need to be updated.

[mmalerba]

@Goobles are you planning to update the tests here?

[Goobles]

@mmalerba Oh, the test that are failing were from tests on experimental components, I don't really know how to change them correctly?

[mmalerba]

@crisbeto are you able to help with getting the tests fixed?

[mmalerba]

It looks like the failure is just rounding issues. You can change the test to do approximate comparison by doing something like Math.abs(expected - actual) < 1

[mmalerba]

LGTM

[andrewseguin]

This ones close to getting in - do you mind rebasing?

[mmalerba]

@andrewseguin I rebased it

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