This stores the wasm object and the function index in the script, and
adds functions to get the disassembled wasm code as well as the offset
table mapping from byte position to line and column in the disassembly
solely from the script.
This will be used to show "ui source code" in DevTools, and map raw
locations from the stack trace into this code view.

R=yangguo@chromium.org, ahaas@chromium.org, titzer@chromium.org
BUG=chromium:613110

patch from issue 2063013004 at patchset 80001 (http://crrev.com/2063013004#ps80001)

Review-Url: https://codereview.chromium.org/2105303002
Cr-Commit-Position: refs/heads/master@{#37430}