Add data MIMEType to navigation context

Bug: 929492
Change-Id: I09d9495606bf416ebb0b6db5135ce5a218139755
Reviewed-on: https://chromium-review.googlesource.com/c/1473172
Commit-Queue: Olivier Robin <olivierrobin@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#633650}
6 files changed