Revert of TaskGraphRunner Group support

cc/raster/single_thread_task_graph_runner.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/raster/single_thread_task_graph_runner.h"
 
 #include <string>
 
 #include "base/threading/simple_thread.h"
 #include "base/threading/thread_restrictions.h"
@@ skipping 94 matching lines @@
   {
     base::AutoLock lock(lock_);
     work_queue_.CollectCompletedTasks(token, completed_tasks);
   }
 }
 
 void SingleThreadTaskGraphRunner::Run() {
   base::AutoLock lock(lock_);
 
   while (true) {
-    if (!RunTaskWithLockAcquired()) {
+    if (!work_queue_.HasReadyToRunTasks()) {
       // Exit when shutdown is set and no more tasks are pending.
       if (shutdown_)
         break;
 
       // Wait for more tasks.
       has_ready_to_run_tasks_cv_.Wait();
       continue;
     }
+
+    RunTaskWithLockAcquired();
   }
 }
 
-bool SingleThreadTaskGraphRunner::RunTaskWithLockAcquired() {
+void SingleThreadTaskGraphRunner::RunTaskWithLockAcquired() {
   TRACE_EVENT0("toplevel",
                "SingleThreadTaskGraphRunner::RunTaskWithLockAcquired");
 
   lock_.AssertAcquired();
 
-  // Find the first category with any tasks to run. This task graph runner
-  // treats categories as an additional priority.
-  const auto& ready_to_run_namespaces = work_queue_.ready_to_run_namespaces();
-  auto found = std::find_if(
-      ready_to_run_namespaces.cbegin(), ready_to_run_namespaces.cend(),
-      [](const std::pair<uint16_t, TaskGraphWorkQueue::TaskNamespace::Vector>&
-             pair) { return !pair.second.empty(); });
-
-  if (found == ready_to_run_namespaces.cend()) {
-    return false;
-  }
-
-  const uint16_t category = found->first;
-  auto prioritized_task = work_queue_.GetNextTaskToRun(category);
+  auto prioritized_task = work_queue_.GetNextTaskToRun();
   Task* task = prioritized_task.task;
 
   // Call WillRun() before releasing |lock_| and running task.
   task->WillRun();
 
   {
     base::AutoUnlock unlock(lock_);
     task->RunOnWorkerThread();
   }
 
   // This will mark task as finished running.
   task->DidRun();
 
   work_queue_.CompleteTask(prioritized_task);
 
   // If namespace has finished running all tasks, wake up origin thread.
   if (work_queue_.HasFinishedRunningTasksInNamespace(
           prioritized_task.task_namespace))
     has_namespaces_with_finished_running_tasks_cv_.Signal();
-
-  return true;
 }
 
 }  // namespace cc