Makes ResourceLoader own handles and return Files

Makes ResourceLoader own handles and return Files

This way it won't leak if destroyed. Also cleaned up html_viewer's use
of ResourceLoader.

R=ben@chromium.org
TBR=ben@chromium.org
BUG=none
TEST=none

Committed: https://crrev.com/6e4a8779b6f3cf90d4d69356f499db025e891c5a
Cr-Commit-Position: refs/heads/master@{#329295}

[sky, 2015-05-11 23:57:48]

I'm TBRing as without this windows is likely broke.

[sky, 2015-05-11 23:58:04]

The CQ bit was checked by sky@chromium.org

[commit-bot: I haz the power, 2015-05-12 00:01:11]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1132083003/20001

[commit-bot: I haz the power, 2015-05-12 00:29:05]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-05-12 00:29:51]

Patchset 2 (id:??) landed as
https://crrev.com/6e4a8779b6f3cf90d4d69356f499db025e891c5a
Cr-Commit-Position: refs/heads/master@{#329295}