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}

diff --git a/cc/BUILD.gn b/cc/BUILD.gn
index 80d3c5e..2afc662 100644
--- a/cc/BUILD.gn
+++ b/cc/BUILD.gn

@@ -377,8 +377,8 @@
     "raster/texture_compressor.h",
     "raster/texture_compressor_etc1.cc",
     "raster/texture_compressor_etc1.h",
-    "raster/tile_task_runner.cc",
-    "raster/tile_task_runner.h",
+    "raster/tile_task.cc",
+    "raster/tile_task.h",
     "raster/tile_task_worker_pool.cc",
     "raster/tile_task_worker_pool.h",
     "raster/zero_copy_tile_task_worker_pool.cc",