Allow the PDF extension to load its plugin correctly

Allow the PDF extension to load its plugin correctly

This changes the PDF extensions CSP so it can correctly load
its plugin. Previously we were loading it as an <object> and
specifying a src attribute which isn't a valid way to load
a plugin and causes some things not to function correctly.
Now we instead load it as an <embed> which can have a src
attribute.

BUG=416328
Committed: https://crrev.com/5075bd244002f56c4bfee1bf869c034118c08c65
Cr-Commit-Position: refs/heads/master@{#305783}

[raymes, 2014-11-25 13:48:16]

raymes@chromium.org changed reviewers:
+ sammc@chromium.org

[Sam McNally, 2014-11-25 22:25:41]

lgtm

[raymes, 2014-11-26 01:05:47]

The CQ bit was checked by raymes@chromium.org

[commit-bot: I haz the power, 2014-11-26 01:07:04]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/754393002/20001

[commit-bot: I haz the power, 2014-11-26 02:08:47]

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

[commit-bot: I haz the power, 2014-11-26 02:08:48]

Try jobs failed on following builders:
  linux_chromium_rel_ng on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)
  mac_chromium_rel_ng on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_...)

[raymes, 2014-11-26 03:12:25]

The CQ bit was checked by raymes@chromium.org

[commit-bot: I haz the power, 2014-11-26 03:12:38]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/754393002/40001

[commit-bot: I haz the power, 2014-11-26 04:44:01]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2014-11-26 04:44:44]

Patchset 3 (id:??) landed as
https://crrev.com/5075bd244002f56c4bfee1bf869c034118c08c65
Cr-Commit-Position: refs/heads/master@{#305783}