Fix `largest-contentful-paint/image-upscaling.html` to use `test_driver.bless` for opening the popup

[smfr]

Test List

largest-contentful-paint/image-upscaling.html

Rationale

This test opens popup windows, which may be blocked by the UA. To avoid blocking, wrap the window.open in a test_driver.bless.

[jgraham]

This seems totally reasonable to me.

[smfr]

Unfortunately it doesn't see to fix the Safari failure; more investigation needed.