cc: Remove ScheduleOnOriginThread() and CompleteOnOriginThread().

cc/raster/gpu_tile_task_worker_pool.cc

Index: cc/raster/gpu_tile_task_worker_pool.cc
diff --git a/cc/raster/gpu_tile_task_worker_pool.cc b/cc/raster/gpu_tile_task_worker_pool.cc
index 858094ea218c143b2e5d180b90bc40893608b780..f2687e2adfb117a413c29363942e8ef2495b63de 100644
--- a/cc/raster/gpu_tile_task_worker_pool.cc
+++ b/cc/raster/gpu_tile_task_worker_pool.cc
@@ -118,7 +118,6 @@ GpuTileTaskWorkerPool::GpuTileTaskWorkerPool(
                                     gpu_rasterization_msaa_sample_count)) {}
 
 GpuTileTaskWorkerPool::~GpuTileTaskWorkerPool() {
-  DCHECK_EQ(0u, completed_tasks_.size());
 }
 
 TileTaskRunner* GpuTileTaskWorkerPool::AsTileTaskRunner() {
@@ -136,8 +135,6 @@ void GpuTileTaskWorkerPool::Shutdown() {
 void GpuTileTaskWorkerPool::ScheduleTasks(TaskGraph* graph) {
   TRACE_EVENT0("cc", "GpuTileTaskWorkerPool::ScheduleTasks");
 
-  ScheduleTasksOnOriginThread(this, graph);
-
   // Barrier to sync any new resources to the worker context.
   rasterizer_->resource_provider()
       ->output_surface()
@@ -148,13 +145,11 @@ void GpuTileTaskWorkerPool::ScheduleTasks(TaskGraph* graph) {
   task_graph_runner_->ScheduleTasks(namespace_token_, graph);
 }
 
-void GpuTileTaskWorkerPool::CheckForCompletedTasks() {
+void GpuTileTaskWorkerPool::CollectCompletedTasks(
+    Task::Vector* completed_tasks) {
   TRACE_EVENT0("cc", "GpuTileTaskWorkerPool::CheckForCompletedTasks");
 
-  task_graph_runner_->CollectCompletedTasks(namespace_token_,
-                                            &completed_tasks_);
-  CompleteTasks(completed_tasks_);
-  completed_tasks_.clear();
+  task_graph_runner_->CollectCompletedTasks(namespace_token_, completed_tasks);
 }
 
 ResourceFormat GpuTileTaskWorkerPool::GetResourceFormat(
@@ -168,15 +163,8 @@ bool GpuTileTaskWorkerPool::GetResourceRequiresSwizzle(
   return false;
 }
 
-void GpuTileTaskWorkerPool::CompleteTasks(const Task::Vector& tasks) {
-  for (auto& task : tasks) {
-    TileTask* tile_task = static_cast<TileTask*>(task.get());
-
-    tile_task->WillComplete();
-    tile_task->CompleteOnOriginThread(this);
-    tile_task->DidComplete();
-  }
-  completed_tasks_.clear();
+TileTaskClient* GpuTileTaskWorkerPool::AsTileTaskClient() {
+  return this;
 }
 
 std::unique_ptr<RasterBuffer> GpuTileTaskWorkerPool::AcquireBufferForRaster(