Add a signal to the scheduler that a navigation is expected

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 bb5dc7224f7cbf2650d316d3e55060fae20b09b2..6aa24a7a46b04fd7b7df099bf2f238b7edecf0c6 100644
--- a/components/scheduler/renderer/renderer_scheduler_impl.cc
+++ b/components/scheduler/renderer/renderer_scheduler_impl.cc
@@ -111,7 +111,8 @@ RendererSchedulerImpl::MainThreadOnly::MainThreadOnly()
       loading_tasks_seem_expensive(false),
       timer_tasks_seem_expensive(false),
       touchstart_expected_soon(false),
-      have_seen_a_begin_main_frame(false) {}
+      have_seen_a_begin_main_frame(false),
+      navigation_expected(false) {}
 
 RendererSchedulerImpl::MainThreadOnly::~MainThreadOnly() {}
 
@@ -593,6 +594,10 @@ void RendererSchedulerImpl::UpdatePolicyLocked(UpdateType update_type) {
   if (!MainThreadOnly().have_seen_a_begin_main_frame)
     block_expensive_tasks = false;
 
+  // Don't block expensive tasks if we are expecting a navigation.
+  if (MainThreadOnly().navigation_expected)
+    block_expensive_tasks = false;
+
   if (block_expensive_tasks && loading_tasks_seem_expensive)
     new_policy.loading_queue_priority = TaskQueue::DISABLED_PRIORITY;
 
@@ -769,6 +774,8 @@ RendererSchedulerImpl::AsValueLocked(base::TimeTicks optional_now) const {
       "rails_loading_priority_deadline",
       (AnyThread().rails_loading_priority_deadline - base::TimeTicks())
           .InMillisecondsF());
+  state->SetBoolean("navigation_expected",
+                    MainThreadOnly().navigation_expected);
   state->SetDouble("last_idle_period_end_time",
                    (AnyThread().last_idle_period_end_time - base::TimeTicks())
                        .InMillisecondsF());
@@ -811,9 +818,23 @@ void RendererSchedulerImpl::OnIdlePeriodEnded() {
   UpdatePolicyLocked(UpdateType::MAY_EARLY_OUT_IF_POLICY_UNCHANGED);
 }
 
-void RendererSchedulerImpl::OnPageLoadStarted() {
+void RendererSchedulerImpl::OnNavigationExpected() {
+  helper_.CheckOnValidThread();
+  base::AutoLock lock(any_thread_lock_);

[Sami, 2015/09/24 15:16:15]

nit: Just call UpdatePolicy() to avoid some boilerplate?

[alex clarke (OOO till 29th), 2015/09/24 15:37:14]

Done.

+  MainThreadOnly().navigation_expected = true;
+  UpdatePolicyLocked(UpdateType::MAY_EARLY_OUT_IF_POLICY_UNCHANGED);
+}
+
+void RendererSchedulerImpl::OnNavigationCanceled() {
+  helper_.CheckOnValidThread();
+  base::AutoLock lock(any_thread_lock_);

[Sami, 2015/09/24 15:16:15]

Ditto.

[alex clarke (OOO till 29th), 2015/09/24 15:37:14]

Done.

+  MainThreadOnly().navigation_expected = false;
+  UpdatePolicyLocked(UpdateType::MAY_EARLY_OUT_IF_POLICY_UNCHANGED);
+}
+
+void RendererSchedulerImpl::OnNavigationStarted() {
   TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("renderer.scheduler"),
-               "RendererSchedulerImpl::OnPageLoadStarted");
+               "RendererSchedulerImpl::OnNavigationStarted");
   base::AutoLock lock(any_thread_lock_);
   AnyThread().rails_loading_priority_deadline =
       helper_.Now() + base::TimeDelta::FromMilliseconds(
@@ -854,6 +875,7 @@ void RendererSchedulerImpl::ResetForNavigationLocked() {
   // Make sure that we don't initially assume there is no idle time.
   MainThreadOnly().short_idle_period_duration.InsertSample(
       cc::BeginFrameArgs::DefaultInterval());
+  MainThreadOnly().navigation_expected = false;
   AnyThread().user_model.Reset();
   MainThreadOnly().have_seen_a_begin_main_frame = false;
   UpdatePolicyLocked(UpdateType::MAY_EARLY_OUT_IF_POLICY_UNCHANGED);