Revert of Use associated interface on DownloadedTempFile

Revert of Use associated interface on DownloadedTempFile (patchset #10 id:180001 of https://codereview.chromium.org/2561743003/ )

Reason for revert:
Culprit suspect for failing ThreadSanitizer tests, e.g. https://uberchromegw.corp.google.com/i/chromium.memory/builders/Linux%20TSan%20Tests/builds/581/steps/content_browsertests/logs/RenderThreadImplBrowserTest.InputHandlerManagerDestroyedAfterCompositorThread

Original issue's description:
> Use associated interface on DownloadedTempFile
> 
> Blob systems depends on the ordering of loading IPC messages. That is,
> the blob creation IPC via XHR is issued before the destruction of
> DownloadedTempFile, and it expects to the blob IPC is handled before
> DownloadedTempFile IPC.
> However in the previous code, that is not guaranteed by Mojo, and that
> makes Layout tests flaky. This CL switches DownLoadedTempFile in a loading
> IPC to an associated interface to ensure it preserves the ordering of IPC
> to other loading IPCs.
> 
> BUG=670562
> 
> Review-Url: https://codereview.chromium.org/2561743003
> Cr-Commit-Position: refs/heads/master@{#445611}
> Committed: https://chromium.googlesource.com/chromium/src/+/ad092abe5691a30391dbc0fd846af75e9917d37b

TBR=yhirano@chromium.org,mmenke@chromium.org,dcheng@chromium.org,yzshen@chromium.org,kinuko@chromium.org,tzik@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=670562

[mastiz, 2017-01-25 09:46:24]

The CQ bit was checked by mastiz@chromium.org

[mastiz, 2017-01-25 09:46:24]

Created Revert of Use associated interface on DownloadedTempFile

[commit-bot: I haz the power, 2017-01-25 09:46:43]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-01-25 09:48:21]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-01-25 09:48:22]

Try jobs failed on following builders:
  ios-device on master.tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/ios-device/builds...)
  ios-device-xcode-clang on master.tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/ios-device-xcode-...)
  ios-simulator on master.tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/ios-simulator/bui...)
  ios-simulator-xcode-clang on master.tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/ios-simulator-xco...)

[mastiz, 2017-01-25 12:47:48]

The CQ bit was checked by mastiz@chromium.org to run a CQ dry run

[mastiz, 2017-01-25 12:48:07]

The CQ bit was unchecked by mastiz@chromium.org