The current logic in Isolate::GetLocationFromStackTrace just ignores
wasm frames, making the computed location point to the first javascript
frame, like this:

test.js:17: RuntimeError: divide by zero
module.exports.main();
               ^
RuntimeError: divide by zero
    at main (<WASM>[1]+5)
    at test.js:17:16

This CL not only fixes the location to point to the top-most wasm
frame, but also exposes to the embedder that the script of that location
is a wasm script, allowing for custom printing of wasm locations.
The Shell::ReportException method now checks for this flag, and prints
wasm locations like this:

<WASM>[0]+5: RuntimeError: divide by zero
RuntimeError: divide by zero
    at main (<WASM>[0]+5)
    at test/message/wasm-trap.js:15:16

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

Review-Url: https://codereview.chromium.org/2563673002
Cr-Commit-Position: refs/heads/master@{#41640}