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This CL uses cursor-compositing to replace the cursor on screen while it
is being dragged.

Originally, when a user drags using the cursor while in capture region
mode, the selected/dragged area lags behind the cursor movements. To
solve that issue, the original screenshot_controller logic hides the
cursor on drag and draws a pseudo cursor directly on the canvas. After
attempting to draw a pseudo cursor on the canvas directly and
encountering issues, it was determined that a better solution would be
to use cursor-compositing, which is what this CL does.

Test: manual, added test
Bug: 1135700
Change-Id: Id35115ab53641c168d8dec4a62756f61d21c967e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2487720
Commit-Queue: Richard Chui <richui@chromium.org>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Reviewed-by: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#820100}