This allows to show wasm source (disassembled wasm code) in DevTools.
See design doc for details.

More tests for the disassembly will have to follow. Also, the text
format (generated by V8) will be changed.

BUG=chromium:659715
R=yangguo@chromium.org, kozyatinskiy@chromium.org, titzer@chromium.org, dgozman@chromium.org

Review-Url: https://codereview.chromium.org/2493773003
Cr-Commit-Position: refs/heads/master@{#41055}