Allow expensive task blocking if there is pending iframe navigation

components/scheduler/renderer/renderer_scheduler_impl.cc

 // Copyright 2014 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 "components/scheduler/renderer/renderer_scheduler_impl.h"
 
 #include "base/bind.h"
 #include "base/debug/stack_trace.h"
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
@@ skipping 1110 matching lines @@
 }
 
 void RendererSchedulerImpl::OnIdlePeriodEnded() {
   base::AutoLock lock(any_thread_lock_);
   AnyThread().last_idle_period_end_time =
       helper_.scheduler_tqm_delegate()->NowTicks();
   AnyThread().in_idle_period = false;
   UpdatePolicyLocked(UpdateType::MAY_EARLY_OUT_IF_POLICY_UNCHANGED);
 }
 
-void RendererSchedulerImpl::AddPendingNavigation() {
+void RendererSchedulerImpl::AddPendingNavigation(bool main_frame_navigating) {
   helper_.CheckOnValidThread();
-  MainThreadOnly().navigation_task_expected_count++;
-  UpdatePolicy();
+  if (main_frame_navigating) {
+    MainThreadOnly().navigation_task_expected_count++;
+    UpdatePolicy();
+  }
 }
 
-void RendererSchedulerImpl::RemovePendingNavigation() {
+void RendererSchedulerImpl::RemovePendingNavigation(
+    bool main_frame_navigating) {
   helper_.CheckOnValidThread();
   DCHECK_GT(MainThreadOnly().navigation_task_expected_count, 0);
-  if (MainThreadOnly().navigation_task_expected_count > 0)
+  if (main_frame_navigating &&
+      MainThreadOnly().navigation_task_expected_count > 0) {
     MainThreadOnly().navigation_task_expected_count--;
-  UpdatePolicy();
+    UpdatePolicy();
+  }
 }
 
 void RendererSchedulerImpl::OnNavigationStarted() {
   TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("renderer.scheduler"),
                "RendererSchedulerImpl::OnNavigationStarted");
   base::AutoLock lock(any_thread_lock_);
   AnyThread().rails_loading_priority_deadline =
       helper_.scheduler_tqm_delegate()->NowTicks() +
       base::TimeDelta::FromMilliseconds(
           kRailsInitialLoadingPrioritizationMillis);
@@ skipping 107 matching lines @@
     }
     MainThreadOnly().have_reported_blocking_intervention_since_navigation =
         true;
     BroadcastConsoleWarning(
         "Deferred long-running timer task(s) to improve scrolling smoothness. "
         "See crbug.com/574343.");
   }
 }
 
 }  // namespace scheduler