DevTools: respect the DOMTokenList.prototype.toggle semantics
DevTools: respect the DOMTokenList.prototype.toggle semantics

Change-Id: I5d67d97c3dc4a852ad516ebb58de1d24bae599e1
Reviewed-on: https://chromium-review.googlesource.com/1154200
Reviewed-by: Aleksey Kozyatinskiy <562acbea96970f508ad9f5cc9fc7c62d82dd3ef8@chromium.org>
Commit-Queue: Pavel Feldman <e1161d7019a0d5c7981e3c3ffc69c76f4b09679a@chromium.org>
Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#578928}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 83a3440044a5789b4525799c9da72d0f51ab6fcc
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