Walk asm.js module ASTs, attach concrete type information
in preparation for generating a WASM module.

cctest test coverage (mjsunit coming in later CL).
Expressions, function tables, and foreign functions have coverage.
Statement coverage to be expanded in a later CL.

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

Review URL: https://codereview.chromium.org/1322773002

Cr-Commit-Position: refs/heads/master@{#30520}