Adding visitors to regurgitate expression types or reset them.

Adding visitors to regurgitate expression types or reset them.

Adding an AstExpressionVisitor to touch each expression node in
an AST.

Adding TypingReseter to clear the slate after a failed asm.js
validation that has set partial typing information.

Adding a ExpressionTypeCollector to walk the expressions
in an AST and emit them as a string for testing.

Adding tests of the above.

LOG=N
BUG= https://code.google.com/p/v8/issues/detail?id=4203
TEST=test-typing-reset,test-ast-expression-visitor
R=rossberg@chromium.org,titzer@chromium.org

Review URL: https://codereview.chromium.org/1288773007

Cr-Commit-Position: refs/heads/master@{#30336}