GitLab

This patch adds checks to see which call site is invoking a
CheckAndIssueSignals without a tile_task_manager_. Code inspection
didn't point at any obvious culprits. Hopefully these checks will.

R=danakj
BUG=642927
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_precise_blink_rel

Review-Url: https://codereview.chromium.org/2341323003
Cr-Commit-Position: refs/heads/master@{#419348}