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This CL makes sure pan, tilt, and zoom can only be set when page is
visible.  When page is hidden, applyConstraints will reject with a
SecurityError for pan, tilt, and zoom only.

Spec: https://github.com/w3c/mediacapture-image/issues/236

Bug: 934063
Change-Id: I442985fabe7337093e336cfd804e405f4c965a12
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2302691Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Commit-Queue: François Beaufort <beaufort.francois@gmail.com>
Cr-Commit-Position: refs/heads/master@{#791211}