scheduler: Add support for tracing scheduler state

content/renderer/scheduler/renderer_scheduler_impl.h

Index: content/renderer/scheduler/renderer_scheduler_impl.h
diff --git a/content/renderer/scheduler/renderer_scheduler_impl.h b/content/renderer/scheduler/renderer_scheduler_impl.h
index 784e2f201c60490db61c10174cd46d6e7a527367..3019fca7855f2e0dea1533a0ee611df5966c5d5b 100644
--- a/content/renderer/scheduler/renderer_scheduler_impl.h
+++ b/content/renderer/scheduler/renderer_scheduler_impl.h
@@ -12,6 +12,12 @@
 #include "content/renderer/scheduler/single_thread_idle_task_runner.h"
 #include "content/renderer/scheduler/task_queue_manager.h"
 
+namespace base {
+namespace debug {
+class ConvertableToTraceFormat;
+}
+}
+
 namespace content {
 
 class RendererTaskQueueSelector;
@@ -58,6 +64,12 @@ class RendererSchedulerImpl : public RendererScheduler,
     COMPOSITOR_PRIORITY_POLICY,
   };
 
+  // Returns the serialized scheduler state for tracing.
+  scoped_refptr<base::debug::ConvertableToTraceFormat> AsValueLocked(
+      base::TimeTicks optional_now) const;
+  static const char* TaskQueueIdToString(QueueId queue_id);
+  static const char* PolicyToString(Policy policy);
+
   // The time we should stay in CompositorPriority mode for after a touch event.
   static const int kCompositorPriorityAfterTouchMillis = 100;