Enforce noopener on cross-top-level-site Blob URLs

[recvfrom]

Enforce noopener on cross-top-level-site Blob URL navigations

This change causes noopener to be set for window.open, clicks
on 'a' / 'area' elements, and form submissions where the corresponding
Blob URL is cross-site to the top-level site of the context performing
the action. This corresponds to the discussion in
w3c/FileAPI#153.

• At least two implementers are interested (and none opposed):
  • WebKit: Blob URL store partitioning w3c/FileAPI#153 (comment)
  • Gecko: Blob URL store partitioning w3c/FileAPI#153 (comment)
  • Chromium: Blob URL store partitioning w3c/FileAPI#153 (comment)
• Tests are written and can be reviewed and commented upon at:
  • https://chromium-review.googlesource.com/c/chromium/src/+/5967596 (with additional tests for the 'a' / 'area' link click noopener changes in https://chromium-review.googlesource.com/c/chromium/src/+/5979376)
• Implementation bugs are filed:
  • Chromium: https://crbug.com/361751872
  • Gecko: https://bugzilla.mozilla.org/show_bug.cgi?id=1928383
  • WebKit: https://bugs.webkit.org/show_bug.cgi?id=282387
  • Deno (only for timers, structured clone, base64 utils, channel messaging, module resolution, web workers, and web storage): N/A
  • Node.js (only for timers, structured clone, base64 utils, channel messaging, and module resolution): N/A
• MDN issue is filed: Note that Blob URL usage is restricted due to storage partitioning mdn/content#36542
• The top of this comment includes a clear commit message to use.

(See WHATWG Working Mode: Changes for more details.)

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