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Since we produce code cache asynchronously, content might
already be invalid, e.g. due to frame detach.

Added a test which catches the issue in 2 of 10 runs.

Bug: none
Change-Id: Ie4368b2a9dce68d236a7310900488056a9e20765
Reviewed-on: https://chromium-review.googlesource.com/c/1483365Reviewed-by: Hiroshige Hayashizaki <hiroshige@chromium.org>
Commit-Queue: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#635153}