MediaDrmBridge: only use delegate init data if non-empty.

MediaDrmBridge: only use delegate init data if non-empty.

R=xhwang@chromium.org
BUG=None
TEST=verified Cast playready test

Committed: https://crrev.com/4614a4f5597f0ec74bcb59e897b1d1ce4cf4dbea
Cr-Commit-Position: refs/heads/master@{#327756}

[gunsch, 2015-04-30 17:08:14]

I had this in the original CL, but it looks like I lost it resolving merge
conflicts (rebasing on the CL that converted all the init_data use from
[pointer+length] to [std::vector])

[xhwang, 2015-04-30 17:44:09]

lgtm

[gunsch, 2015-04-30 18:04:24]

The CQ bit was checked by gunsch@chromium.org

[commit-bot: I haz the power, 2015-04-30 18:05:22]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1113023004/1

[commit-bot: I haz the power, 2015-04-30 19:07:03]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-30 19:08:10]

Patchset 1 (id:??) landed as
https://crrev.com/4614a4f5597f0ec74bcb59e897b1d1ce4cf4dbea
Cr-Commit-Position: refs/heads/master@{#327756}