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FrameTypeTopLevel in this case will be considered bad message by PlzNavigate.

This fixes browser tests with PlzNavigate:
ErrorPageTest.DNSError_DoClickLink
ErrorPageTest.DNSError_DoReload
ErrorPageTest.DNSError_DoReloadAfterSamePageNavigation
ErrorPageTest.DNSError_DoSearch
ErrorPageTest.StaleCacheStatus

BUG=576285

Review-Url: https://codereview.chromium.org/2285493002
Cr-Commit-Position: refs/heads/master@{#414660}