cc: Add a resource_provider_ dcheck in resource_pool creation.

cc: Add a resource_provider_ dcheck in resource_pool creation.

This patch just adds one DCHECK in order to help diagnose a crash that
seems to happen when we create a resource_pool with a null resource
provider.

R=enne
BUG=419086
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Committed: https://crrev.com/7baed6836b25569063305363e9c6f7b7169853e1
Cr-Commit-Position: refs/heads/master@{#339747}

[vmpstr, 2015-07-20 23:17:13]

Please take a look.

[enne (OOO), 2015-07-20 23:20:41]

Should this be a temporary CRASH if you're trying to diagnose this?

[vmpstr, 2015-07-21 17:24:18]

PTAL

[enne (OOO), 2015-07-21 19:04:15]

lgtm

[vmpstr, 2015-07-21 19:48:20]

The CQ bit was checked by vmpstr@chromium.org

[commit-bot: I haz the power, 2015-07-21 19:49:13]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1243773003/40001

[commit-bot: I haz the power, 2015-07-21 21:12:08]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-07-21 21:13:05]

Patchset 3 (id:??) landed as
https://crrev.com/7baed6836b25569063305363e9c6f7b7169853e1
Cr-Commit-Position: refs/heads/master@{#339747}