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As discussed on the security review this CL adds the following mitigations:
- require a transient user activation on the browser side, and consume
it when showing the eye dropper for the renderer (this will prevent a
compromised renderer to repeatedly ask for a color)
- require the eye dropper UI to be visible for a minimum amount of time
before color selection is allowed in order to ensure the user has a
chance to see the UI.

There is also a fix for the popup not correctly updating the user
activation state. This happens because it is using a
EmptyLocalFrameClient and its frame is not related to the
owner element's frame.

Bug: 992297
Change-Id: Ia5d2aead0be153ce4b49048552062de3a6c72e63
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2442132Reviewed-by: Kent Tamura <tkent@chromium.org>
Reviewed-by: Mason Freed <masonfreed@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Mason Freed <masonfreed@chromium.org>
Cr-Commit-Position: refs/heads/master@{#812847}