This API allows clients to specify which view should be considered as the tracking scroll view for the bottom sheet gestural behaviors.
The API name is consistent with the FlexibleHeader component's similar API.
* First bottom sheet commit
* Add empty files of needed classes
* Do animation using presentation controller and transitioning delegate
* Implement bottom sheet transition using just a UIPresentationController
* Tap background to dismiss
* Clean up and document bottom sheet interface
* Minor cleanup
* Fix usePreferredHeight
* Toggle usePreferredHeight
* Let UIPresentationController layout sheet view
* Expand bottom sheet delegate api
* Remove automaticallyDismissBottomSheet and usePreferredHeight
* Remove shouldDismiss
* Delegate method docs
* Allow custom bottom sheet widths
* Animate sheet view to new frame when rotating bottom sheet
* Fix sheet view starting in bad location
* Specify float for background color
* Clean up bottom sheet presentation controller
* Minor cleanup
* Copy cl/148818444
* GOO -> MDC
* s/draging/dragging/
* Use init instead of initWithCoder
* Bottom sheet example description
* Big improvements to bottom sheet examples
* MDCBottomSheetTransitionController
* Wrap up everything in MDCBottomSheetViewController
* Move all examples to MDCBottomSheetViewController
* Move supplemental code to BottomSheetSupplemental
* bottomSheetPresentationControllerDidDismissBottomSheet
* Check delegate implements methods before calling
* MDCBottomSheetViewController -> MDCBottomSheetController
* Add comments for MDCBottomSheetController
* Use MDCMath
* Change style of preferredContentSize setter
* Support preferredContentSize.height
* Add an example layed out using Autolayout
* More correctly set frame for non scrolling content
* Minor improvements to examples
* Small fixes for examples
* Use umbrella import headers
* Show custom preferredContentSize width in example
* MDCBottomSheetTransitionController now vends a presentation controller
* Expose bottom sheet presentation controller on UIViewController
* Final review comments