miguely 2d618793dd Adds support for more than one expanded state for the BackLayerLayout.
The content for the backlayer should be able to change in runtime to allow for multiple experiences in the backlayer. Furthermore, changing to a different experience should not imply collapsing and re-expanding the backlayer, it should happen in-place with the content layer sliding to accommodate the size of the new content.

If expand is called when the backlayer is already expanded then the backlayer
animates a possible size change.

If there is no need to change the size then the duration for the animation is
zero.

On the side, this changes BackLayer to be a LinearLayout.

PiperOrigin-RevId: 162277051
2017-09-21 12:00:21 -04:00
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