GitLab

The Blob type was serialized/restored correctly on the Blink side, but
not on the Chromium side, so when reading a Blob as a stream the
type would be unset.

BUG=408120
R=cmumford@chromium.org
TEST=https://codereview.chromium.org/509213005

Review URL: https://codereview.chromium.org/511373002

Cr-Commit-Position: refs/heads/master@{#292485}