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For the help of comparing two implementation design of "Imperative Shadow DOM
Distribution API", this CL introduces some performance tests.

Some of the tests are micro benchmark tests for each function, assign, assignSlot, assignElements,
insertBefore, and appendChild, that manual slotting mode uses.
In another tests, the performance of the new custom element, <my-detail>/<my-summary> are testes
when assigned nodes are over 100.
In addition, some algorithm　for the new custom element are added to do the previous tests.

Bug: 869308
Change-Id: Ib2ad2f2ea304d0f7ddbb25b5b85e739af7ee465b
Reviewed-on: https://chromium-review.googlesource.com/1214964
Commit-Queue: Kyoko Muto <kymuto@google.com>
Reviewed-by: Hayato Ito <hayato@chromium.org>
Cr-Commit-Position: refs/heads/master@{#591293}