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This add layout tests to ensure javascript code caching is working as
expected. This also adds virtual tests with (
--enable-features=IsolatedCodeCache --site-per-process) to test that the
isolated code cache is behaving as expected. These tests test that:
1. code cache is created on the second visit to the script
2. code cache is consumed on the third visit to the script
3. code cache for the same script resource is not reused if
requested from a different origin (for the virtual tests).

Bug: chromium:879494
Change-Id: I05f92fa129dac2419c84fcc65e9d0c684b9d48e2
Reviewed-on: https://chromium-review.googlesource.com/c/1297363Reviewed-by: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Commit-Queue: Mythri Alle <mythria@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604199}