Reenabling DomSerializerTests that were "temporarily" disabled...
Reenabling DomSerializerTests that were "temporarily" disabled...

Note1: The merge of the serializers got reverted (crrev.com/1295063002).
As part of the revert we should have reenabled the tests.

Note2: For the long-term such temporary disabling of tests will not be
needed anymore, because now Chromium and Blink are in the same repo.

BUG=328354

Review URL: https://codereview.chromium.org/1575173002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#368957}

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