Note we remove the call to mChannel->SetContentType() from RecreateChannel().
The hint never works as expected for [1] is the only caller to
nsIChannel::GetContentType() and MediaResource::Create() always happens
before any reads from the resource.
[1] http://searchfox.org/mozilla-central/rev/b425854d9bbd49d5caf9baef3686e49ec91c17ec/dom/media/MediaResource.cpp#1500
MozReview-Commit-ID: 1n4yHEouCjC
--HG--
extra : rebase_source : 9a7345c29b985ddee7a90a94191e9d526e2a0a67
extra : source : 054d9ffaf21eb937a6349df76228269ad2d7dc2c