dart2wasm compilation tests

[elliette]

We don't currently have any tests for our wasm-compiled app besides our benchmark tests.

Ideally, I would like to have a test that:

1. serves devtools in release mode
2. modifies the query parameter (to either compiler=wasm or compiler=js)
3. verifies devtools is now using the wasm or js compilation
4. verifies the local storage file containing the users preference now contains either wasm or js

This likely will need a new test setup to serve DevTools in release build. I'm not sure the best package for this, whether we should be using integration_test or webdriver.

[elliette]

See testing comment here as well #9406 (review)

[elliette]

Note: Due to #9197, we cannot test our release app running on the DevTools server until DevTools is moved into the Dart SDK.

Therefore, the PR above adds a test that verifies the compiler query params work for the DevTools version bundled with the SDK. Although this means we won't be able to catch regressions until after they have landed, it does give us some security here that we will catch regressions before they affect users.

Once DevTools is moved into the Dart SDK, we can update the test.