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From https://www.w3.org/TR/mediacapture-streams/ To apply the
ApplyConstraints algorithm to an object. We need to remove the
existing constraints from object.

Bug: b:151048287
Test: Tested on kukui and eve.
Change-Id: I711a1e6dff9ae9dc77fc622cddfac07ceace12b4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2386918Reviewed-by: Wei Lee <wtlee@chromium.org>
Commit-Queue: Hsu Wei-Cheng <mojahsu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804659}