This patch makes it easier to use the auto layout API:
* We no longer use operator== because that requires an ugly cast by the
API user.
* Also, "leftEdge" is now just "left" for less verbosity.
* AutoLayoutChild not implies its key from the AutoLayoutParam object.
* We now correctly layout every child of a RenderAutoLayout object even
if the solver doesn't flush any updates to that child.
c7d71d8ab1