This change rewrites simple and safe Expression<Func<T, U>> expressions
into accesses to readonly fields. This allows us to cache the actual
expression and avoid repeatedly allocating and compiling it.
The rewrite is limited to cases where we know that the expression doesn't
capture, and where we support that kind of expression for evaluating
viewdata. In practice this means 'indentity' and property accessors are
allowed.
Pavel Krymets
Ryan Nowak