Remove dependency of history_unittests on content::DownloadInterruptReason

Remove dependency of history_unittests on content::DownloadInterruptReason

Export kTestDownloadInterruptReason{None,Crash} and use them in
history_unittests.cc to remove dependency on content::DownloadInterruptReason.

Remove unused #includes.

BUG=370850
Committed: https://crrev.com/2f6155f7d07aed46cdce253445ab6ac08b3b2ac9
Cr-Commit-Position: refs/heads/master@{#326805}

[sdefresne, 2015-04-24 14:39:44]

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

[commit-bot: I haz the power, 2015-04-24 14:40:12]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1107683003/1

[sdefresne, 2015-04-24 14:42:08]

sdefresne@chromium.org changed reviewers:
+ droger@chromium.org

[sdefresne, 2015-04-24 14:42:08]

PTAL

[droger, 2015-04-24 14:44:20]

lgtm

[sdefresne, 2015-04-24 14:49:56]

The CQ bit was unchecked by sdefresne@chromium.org

[sdefresne, 2015-04-24 14:51:12]

The CQ bit was checked by sdefresne@chromium.org

[sdefresne, 2015-04-24 14:51:13]

The patchset sent to the CQ was uploaded after l-g-t-m from droger@chromium.org
Link to the patchset: https://codereview.chromium.org/1107683003/#ps20001
(title: "Remove duplicate #include")

[commit-bot: I haz the power, 2015-04-24 14:51:23]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1107683003/20001

[commit-bot: I haz the power, 2015-04-24 15:46:37]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-04-24 15:47:37]

Patchset 2 (id:??) landed as
https://crrev.com/2f6155f7d07aed46cdce253445ab6ac08b3b2ac9
Cr-Commit-Position: refs/heads/master@{#326805}