[scheduler] Disable load throttling for pages with active connection.

Do not apply resource load throttling to background pages with active
websocket or webrtc connection to prevent breakage and disconnects.

Change-Id: Ifd603a2b55cae415b113095df9145217da2b4196
Reviewed-on: https://chromium-review.googlesource.com/1042313Reviewed-by: Takashi Toyoshima <toyoshim@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Alexander Timin <altimin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558340}

third_party/blink/renderer/platform/scheduler/main_thread/frame_scheduler_impl.cc

@@ -589,11 +589,19 @@ void FrameSchedulerImpl::NotifyThrottlingObservers() {
 
 FrameScheduler::ThrottlingState FrameSchedulerImpl::CalculateThrottlingState(
     ObserverType type) const {
+  // Detached frames are not throttled.
+  if (!parent_page_scheduler_)
+    return FrameScheduler::ThrottlingState::kNotThrottled;
+
   if (RuntimeEnabledFeatures::StopLoadingInBackgroundEnabled() &&
       page_frozen_ && !keep_active_) {
     DCHECK(page_visibility_ == PageVisibilityState::kHidden);
     return FrameScheduler::ThrottlingState::kStopped;
   }
+  if (type == ObserverType::kLoader &&
+      parent_page_scheduler_->HasActiveConnection()) {
+    return FrameScheduler::ThrottlingState::kNotThrottled;
+  }
   if (page_visibility_ == PageVisibilityState::kHidden)
     return FrameScheduler::ThrottlingState::kThrottled;
   return FrameScheduler::ThrottlingState::kNotThrottled;

third_party/blink/renderer/platform/scheduler/main_thread/page_scheduler_impl.cc

@@ -275,6 +275,10 @@ bool PageSchedulerImpl::IsExemptFromBudgetBasedThrottling() const {
 }
 
 bool PageSchedulerImpl::HasActiveConnectionForTest() const {
+  return HasActiveConnection();
+}
+
+bool PageSchedulerImpl::HasActiveConnection() const {
   return has_active_connection_;
 }
 
@@ -299,6 +303,7 @@ void PageSchedulerImpl::OnConnectionUpdated() {
 
   if (has_active_connection_ != has_active_connection) {
     has_active_connection_ = has_active_connection;
+    UpdateFramePolicies();
     UpdateBackgroundThrottlingState();
   }
 }

third_party/blink/renderer/platform/scheduler/main_thread/page_scheduler_impl.h

@@ -75,6 +75,9 @@ class PLATFORM_EXPORT PageSchedulerImpl : public PageScheduler {
   virtual void ReportIntervention(const std::string& message);
 
   bool IsFrozen() const;
+  // PageSchedulerImpl::HasActiveConnection can be used in non-test code,
+  // while PageScheduler::HasActiveConnectionForTest can't.
+  bool HasActiveConnection() const;
 
   std::unique_ptr<FrameSchedulerImpl> CreateFrameSchedulerImpl(
       base::trace_event::BlameContext*,