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This is to add cdp support for the frontend to send window segments
info to the backend, to be consumed by the platform.

The explainer for window segments is at:
Explainer:  https://github.com/webscreens/window-segments/blob/master/EXPLAINER.md

During discussion of the dual screen explainer, it was agreed that the
change will be reviewed at CR time. The explainer is at:
https://docs.google.com/document/d/1KMsmEXdjmn4h4iIl0n74N1EHxwwNUzh6R2p7GHrdtTI/

This change can be tested with web_tests. But it relies on a frontend
CL and one more platform CL for a user to see the effect. The frontend
CL (WIP) is at:
https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2245774

The platform CL:

https://chromium-review.googlesource.com/c/chromium/src/+/2262193

Change-Id: I6309b8bea0b24b0d098a82a02045115f00d2b34f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2248131Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Reviewed-by: Will Harris <wfh@chromium.org>
Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Songtao Xia <soxia@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#786932}