Revert of TaskGraphRunner Group support

cc/raster/synchronous_task_graph_runner.cc

Index: cc/raster/synchronous_task_graph_runner.cc
diff --git a/cc/raster/synchronous_task_graph_runner.cc b/cc/raster/synchronous_task_graph_runner.cc
index 156ef9acda846f0d2ef840ecee922d2aa3e69869..ed05cfb5823127277020491b4b5fbb0d6e3abbd2 100644
--- a/cc/raster/synchronous_task_graph_runner.cc
+++ b/cc/raster/synchronous_task_graph_runner.cc
@@ -3,9 +3,6 @@
 // found in the LICENSE file.
 
 #include "cc/raster/synchronous_task_graph_runner.h"
-
-#include <algorithm>
-#include <utility>
 
 #include "base/threading/simple_thread.h"
 #include "base/threading/thread_restrictions.h"
@@ -44,9 +41,9 @@
   if (!task_namespace)
     return;
 
-  while (!work_queue_.HasFinishedRunningTasksInNamespace(task_namespace)) {
-    bool succeeded = RunTask();
-    DCHECK(succeeded);
+  while (
+      !TaskGraphWorkQueue::HasFinishedRunningTasksInNamespace(task_namespace)) {
+    RunTask();
   }
 }
 
@@ -60,27 +57,14 @@
 }
 
 void SynchronousTaskGraphRunner::RunUntilIdle() {
-  while (RunTask()) {
-  }
+  while (work_queue_.HasReadyToRunTasks())
+    RunTask();
 }
 
-bool SynchronousTaskGraphRunner::RunTask() {
+void SynchronousTaskGraphRunner::RunTask() {
   TRACE_EVENT0("toplevel", "SynchronousTaskGraphRunner::RunTask");
 
-  // 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;
   task->WillRun();
@@ -88,8 +72,6 @@
   task->DidRun();
 
   work_queue_.CompleteTask(prioritized_task);
-
-  return true;
 }
 
 }  // namespace cc