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* Use directory structure to group the generators
* Separate test inputs/expectations from chain generation
* Use a simple CERTIFICATE sequence for chains, since test file carries other information.

This decoupling makes it easier to re-use the chain generation code elsewhere, as well as to have tests that use the same chain but with different input parameters to certificate verification.

Review-Url: https://codereview.chromium.org/2805213004
Cr-Commit-Position: refs/heads/master@{#468857}