Assert that loading is complete in SVGImage::hasSingleSecurityOrigin()
Assert that loading is complete in SVGImage::hasSingleSecurityOrigin()

This patch adds an assert that the "inner page" in an SVGImage has
loaded and does not have any pending subresource loads.

NOTRY=true
BUG=249037

Review URL: https://chromiumcodereview.appspot.com/22999031

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@157433 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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