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Remove the IsolatedWorldCSP blink runtime feature and have the isolated
world CSP always enforced. The current behavior when the
IsolatedWorldCSP feature is disabled, is to just bypass the main world
CSP for clients which set the isolated world CSP.

For the most part, there shouldn't be any behavior change. Currently
there are 3 blink clients which set an isolated world CSP:

- Mv2 extensions specify an empty CSP, so there shouldn't be any
behavior change for them. The empty CSP should behave the same as the
main world CSP being bypassed.

- The translate component does set a non-empty CSP. To preserve the same
behavior we change it's CSP to an empty one.

- Mv3 extensions specify a non-empty CSP and this CSP will now be
enforced in isolated worlds, which is what we want.

BUG=896041

Change-Id: I9c5bf6cff5dda6f5ee9090a873c9fcbc42eab317
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2439540
Auto-Submit: Karan Bhatia <karandeepb@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Takashi Toyoshima <toyoshim@chromium.org>
Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Yuki Shiino <yukishiino@chromium.org>
Commit-Queue: Karan Bhatia <karandeepb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#815474}