730a49b98d
Also, fixes the stocks list to work properly including hit testing at the bottom of the screen. New classes: RenderViewport: a class that supports positioning a child inside itself and offsetting it. Viewport: a RenderObjectWrapper that wraps RenderViewport. ScrollableViewport: a Component that hooks Viewport up to some scrolling behaviour. Code changes: RenderBlock now only works when it has an unbounded height constraint. I removed the clipping in there since it's no longer needed. I made FixedHeightScrollable use Viewport instead of hand-rolling its clipping with Transform and Clip. This is what fixes the stocks list hit testing at the bottom of the screen. I made anywhere that used to use Block now use ScrollableViewport. RenderFlex now takes a list of children. Justifications for test changes: tests/examples/stocks: changing FixedHeightScrollable to use a RenderViewport instead of a RenderClipRect/RenderTransform combination removes the use of an actual transform. R=abarth@chromium.org Review URL: https://codereview.chromium.org/1223153004 .