cc: Merge TileTaskRunner to TileTaskWorkerPool.

This patches merges all interface functions of TileTaskRunner to
TileTaskWorkerPool.

BUG=599863
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1888713002

Cr-Commit-Position: refs/heads/master@{#388430}
30 files changed