DCHECK that scheduler tasks have positive duration.

third_party/WebKit/Source/platform/scheduler/renderer/renderer_scheduler_impl.cc

Index: third_party/WebKit/Source/platform/scheduler/renderer/renderer_scheduler_impl.cc
diff --git a/third_party/WebKit/Source/platform/scheduler/renderer/renderer_scheduler_impl.cc b/third_party/WebKit/Source/platform/scheduler/renderer/renderer_scheduler_impl.cc
index 37ec1fbd3bc120f48bf957d4aead6abe82368bbc..655855104a26d2fd8fa79bc3a43fcd60debf1ce2 100644
--- a/third_party/WebKit/Source/platform/scheduler/renderer/renderer_scheduler_impl.cc
+++ b/third_party/WebKit/Source/platform/scheduler/renderer/renderer_scheduler_impl.cc
@@ -1909,6 +1909,7 @@ void RendererSchedulerImpl::WillProcessTask(TaskQueue* task_queue,
 void RendererSchedulerImpl::DidProcessTask(TaskQueue* task_queue,
                                            double start_time,
                                            double end_time) {
+  DCHECK_LE(start_time, end_time);
   // TODO(scheduler-dev): Remove conversions when Blink starts using
   // base::TimeTicks instead of doubles for time.
   base::TimeTicks start_time_ticks =