TaskGraphRunner Group support

cc/raster/synchronous_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/synchronous_task_graph_runner.h"
 
 #include "base/threading/simple_thread.h"
 #include "base/threading/thread_restrictions.h"
 #include "base/trace_event/trace_event.h"
+#include "cc/raster/task_category.h"
 
 namespace cc {
 
 SynchronousTaskGraphRunner::SynchronousTaskGraphRunner() {}
 
 SynchronousTaskGraphRunner::~SynchronousTaskGraphRunner() {
   DCHECK(!work_queue_.HasReadyToRunTasks());
 }
 
 NamespaceToken SynchronousTaskGraphRunner::GetNamespaceToken() {
@@ skipping 37 matching lines @@
 }
 
 void SynchronousTaskGraphRunner::RunUntilIdle() {
   while (work_queue_.HasReadyToRunTasks())
     RunTask();
 }
 
 void SynchronousTaskGraphRunner::RunTask() {
   TRACE_EVENT0("toplevel", "SynchronousTaskGraphRunner::RunTask");
 
-  auto prioritized_task = work_queue_.GetNextTaskToRun();
+  // Find the first category with any tasks to run. Categories used by this task
+  // graph runner are ordered by priority.
+  uint16_t category;
+  for (category = 0u; category < kNumTaskCategories; ++category) {

[reveman, 2015/12/10 16:49:57]

I'd like to avoid making the kNumTaskCategories assumption. See my other
comment.

[ericrk, 2015/12/14 19:40:57]

What do you think about this approach? It's a bit annoying that we have to do
find_if (as we can't just take the first one, as the list could be empty) - I
thought about trying to write some sort of iterator adapter to just show
non-empty elements, but seemed like more trouble than it was worth.

+    if (work_queue_.HasReadyToRunTasksForCategory(category))
+      break;
+  }
+  DCHECK(category < kNumTaskCategories);
+
+  auto prioritized_task = work_queue_.GetNextTaskToRun(category);
 
   Task* task = prioritized_task.task;
   task->WillRun();
   task->RunOnWorkerThread();
   task->DidRun();
 
   work_queue_.CompleteTask(prioritized_task);
 }
 
 }  // namespace cc