Add testRunner.runIdleTasks() to force idle tasks to run.

components/scheduler/renderer/renderer_scheduler_impl.cc

Index: components/scheduler/renderer/renderer_scheduler_impl.cc
diff --git a/components/scheduler/renderer/renderer_scheduler_impl.cc b/components/scheduler/renderer/renderer_scheduler_impl.cc
index 306c45cc0a783df4c849963c17ec761c1dc2a490..9f3d9b6ef21a16711e52ff193531d3459aed5064 100644
--- a/components/scheduler/renderer/renderer_scheduler_impl.cc
+++ b/components/scheduler/renderer/renderer_scheduler_impl.cc
@@ -126,7 +126,8 @@ RendererSchedulerImpl::MainThreadOnly::MainThreadOnly(
       have_reported_blocking_intervention_since_navigation(false),
       has_visible_render_widget_with_touch_handler(false),
       begin_frame_not_expected_soon(false),
-      expensive_task_blocking_allowed(true) {}
+      expensive_task_blocking_allowed(true),
+      in_idle_period_for_testing(false) {}
 
 RendererSchedulerImpl::MainThreadOnly::~MainThreadOnly() {}
 
@@ -383,12 +384,22 @@ void RendererSchedulerImpl::OnRendererForegrounded() {
 }
 
 void RendererSchedulerImpl::EndIdlePeriod() {
+  if (MainThreadOnly().in_idle_period_for_testing)
+    return;
   TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("renderer.scheduler"),
                "RendererSchedulerImpl::EndIdlePeriod");
   helper_.CheckOnValidThread();
   idle_helper_.EndIdlePeriod();
 }
 
+void RendererSchedulerImpl::EndIdlePeriodForTesting(
+    const base::Closure& callback,
+    base::TimeTicks time_remaining) {
+  MainThreadOnly().in_idle_period_for_testing = false;
+  EndIdlePeriod();
+  callback.Run();
+}
+
 // static
 bool RendererSchedulerImpl::ShouldPrioritizeInputEvent(
     const blink::WebInputEvent& web_input_event) {
@@ -574,6 +585,16 @@ base::TimeTicks RendererSchedulerImpl::CurrentIdleTaskDeadlineForTesting()
   return idle_helper_.CurrentIdleTaskDeadline();
 }
 
+void RendererSchedulerImpl::RunIdleTasksForTesting(
+    const base::Closure& callback) {
+  MainThreadOnly().in_idle_period_for_testing = true;
+  IdleTaskRunner()->PostIdleTask(
+      FROM_HERE,
+      base::Bind(&RendererSchedulerImpl::EndIdlePeriodForTesting,
+                 weak_factory_.GetWeakPtr(), callback));
+  idle_helper_.EnableLongIdlePeriod();
+}
+
 void RendererSchedulerImpl::MaybeUpdatePolicy() {
   helper_.CheckOnValidThread();
   if (policy_may_need_update_.IsSet()) {