swift234

Added a new AST transformation pass called the
"Playground Transform."  This is an
instrumentation pass that adds calls to a
function called playground_log at locations of
interest.  Roughly speaking, these locations are

- Initialization of variables
- Modification of variables
- Expressions returning values
- Application of mutating methods on objects

The playground transform currently only finds
modifications of variables, but the intent is to
make all of these cases work.

It is enabled by a frontend option, and can
also be invoked by calling

swift::performPlaygroundTransform(SF)

which is the way LLDB, its main client, will
use it.

The frontend option is intended for testing,
and indeed I will add tests for this
transformation in the coming week as I bring
more functionality online.


Swift SVN r14801