[WebAssembly] Start a field trial for Wasm compiled code caching

This CL depends on blink::features::kWasmCodeCache:
https://chromium-review.googlesource.com/c/chromium/src/+/1341071

...and hooking up Wasm's site isolated code cache instance:
https://chromium-review.googlesource.com/c/chromium/src/+/1260209

Both of these should land before this one.

Bug: chromium:719172
Change-Id: Ia721e931fb34c6ee3a4346f4b151ce316bc6501c
Reviewed-on: https://chromium-review.googlesource.com/c/1341076
Reviewed-by: Brian White <bcwhite@chromium.org>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#629708}
1 file changed