scheduler: Turn expensive task blocking into a finch trial

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/trace_event/trace_event.h"
@@ skipping 109 matching lines @@
       renderer_hidden(false),
       renderer_backgrounded(false),
       timer_queue_suspension_when_backgrounded_enabled(false),
       timer_queue_suspended_when_backgrounded(false),
       was_shutdown(false),
       loading_tasks_seem_expensive(false),
       timer_tasks_seem_expensive(false),
       touchstart_expected_soon(false),
       have_seen_a_begin_main_frame(false),
       has_visible_render_widget_with_touch_handler(false),
-      begin_frame_not_expected_soon(false) {}
+      begin_frame_not_expected_soon(false),
+      expensive_task_blocking_allowed(true) {}
 
 RendererSchedulerImpl::MainThreadOnly::~MainThreadOnly() {}
 
 RendererSchedulerImpl::AnyThread::AnyThread()
     : awaiting_touch_start_response(false),
       in_idle_period(false),
       begin_main_frame_on_critical_path(false),
       last_gesture_was_compositor_driven(false),
       have_seen_touchstart(false) {}
 
@@ skipping 570 matching lines @@
 
     case UseCase::LOADING:
       new_policy.loading_queue_priority = TaskQueue::HIGH_PRIORITY;
       new_policy.default_queue_priority = TaskQueue::HIGH_PRIORITY;
       break;
 
     default:
       NOTREACHED();
   }
 
+  if (!MainThreadOnly().expensive_task_blocking_allowed) {
+    block_expensive_loading_tasks = false;
+    block_expensive_timer_tasks = false;
+  }
+
   // Don't block expensive tasks unless we have actually seen something.
   if (!MainThreadOnly().have_seen_a_begin_main_frame) {
     block_expensive_loading_tasks = false;
     block_expensive_timer_tasks = false;
   }
 
   // Don't block expensive tasks if we are expecting a navigation.
   if (MainThreadOnly().navigation_task_expected_count > 0) {
     block_expensive_loading_tasks = false;
     block_expensive_timer_tasks = false;
@@ skipping 345 matching lines @@
 }
 
 void RendererSchedulerImpl::RegisterTimeDomain(TimeDomain* time_domain) {
   helper_.RegisterTimeDomain(time_domain);
 }
 
 void RendererSchedulerImpl::UnregisterTimeDomain(TimeDomain* time_domain) {
   helper_.UnregisterTimeDomain(time_domain);
 }
 
+void RendererSchedulerImpl::SetExpensiveTaskBlockingAllowed(bool allowed) {
+  MainThreadOnly().expensive_task_blocking_allowed = allowed;
+}
+
 base::TickClock* RendererSchedulerImpl::tick_clock() const {
   return helper_.scheduler_tqm_delegate().get();
 }
 
 }  // namespace scheduler