Indexed DB: Restore content-type to deserialized Blobs
Indexed DB: Restore content-type to deserialized Blobs

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}
(cherry picked from commit 8f40e3267a13eb1ba11c813a5013d188ed9cb9e2)

Conflicts:
	content/browser/indexed_db/indexed_db_callbacks.cc

Review URL: https://codereview.chromium.org/538693002

Cr-Commit-Position: 0d344d3782ceeadf0e8e8be3f4ce70193b218c54@{#204}
Cr-Branched-From: 2cb3f0147827a1600e8cbbcc52ca24c0febcb7a4@{#290040}

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