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This CL adds metrics to measure the usage of features that require permissions
in Chrome when they are used in cross-origin iframes only. In particular we only
want to count an iframe if it doesn't have scripting access into the top level
document. A new UseCounter::countCrossOriginIframe function has been added which
will only count this type of usage.

Note that this intends to count cases when a site tries to use an API whether or
not the permission is granted by the user.

BUG=444744

Review URL: https://codereview.chromium.org/1578263006

Cr-Commit-Position: refs/heads/master@{#371756}