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This change restrictes the SMS Receiver API to only be used from top level
frames to prevent malicious sites from accessing the one time passcodes
for signup. Restriction in the browser process will be added in a
following CL.

Bug: 955765
Change-Id: Ie11e3b1fc6c9bf4597bde880d5083fec7255b79a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1594211Reviewed-by: Reilly Grant <reillyg@chromium.org>
Commit-Queue: Ayu Ishii <ayui@chromium.org>
Cr-Commit-Position: refs/heads/master@{#658694}