Allows about:blank to load in current tab without going to server
Allows about:blank to load in current tab without going to server

about:blank navigations shouldn't require going to the server as they
are considered same origin.

BUG=479172,490221
TEST=none
R=fsamuel@chromium.org

Review URL: https://codereview.chromium.org/1337883003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#348405}

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