Cleanup DCHECK style in ResourceScheduler

Cleanup DCHECK style in ResourceScheduler

From
https://www.chromium.org/developers/coding-style#TOC-CHECK-DCHECK-and-NOTREACHED-

"... you should not handle DCHECK() failures, even if failure would
result in a crash."

ResourceScheduler contains a number of instances where it attempts to
recover from a DCHECK() failure.

This is part 1 of a two-part cleanup:

Part 1) Remove the recovery code, and replace the DCHECKs with CHECKs to
make sure that the recovery code was really dead.
Part 2) After confirming there are no new crashes from the CHECK()
statements, convert them back to DCHECK()s.

Also fix some lint errors (add #includes for <string> and <vector> and
move a * next to the type in a declaration).

TEST=content_unittests
BUG=526565

Review URL: https://codereview.chromium.org/1321003003

Cr-Commit-Position: refs/heads/master@{#348898}