[caching] Use V8 WASM caching API in Blink

- Removes MainThread restriction for using Mojo caching API. WebAssembly
  streaming instantiation runs off the main thread.
- Adds trace events for streaming instantiation events of interest, which
  are disabled by default.
- Uses the Mojo caching API for WebAssembly streaming compilation, and
  caches modules over 128 KB in size.
- Adds web tests that use the tracing events to make sure caching is
  working correctly.
- Adds two .wasm files, above and below the caching threshold size,
  (128 KB).

Bug: chromium:719172
Change-Id: Iaf7e2fa96e9bb441bda18b780ae41794af119900
Reviewed-on: https://chromium-review.googlesource.com/c/1260209
Commit-Queue: Bill Budge <bbudge@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Alexei Filippov <alph@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Mythri Alle <mythria@chromium.org>
Cr-Commit-Position: refs/heads/master@{#626755}
14 files changed