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This removes DebugDevToolsInterceptor and supports DEBUG_DEVTOOLS
layout as part of regular DevToolsDataSource.

Change-Id: I06d5a805ff8b6b324127b131bb87801d3595311f
Reviewed-on: https://chromium-review.googlesource.com/1229198Reviewed-by: Matt Menke <mmenke@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Andrey Kosyakov <caseq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#592091}