[scheduler] Add unthrottled-by-blockable task queue to fix touch latency regression.

third_party/WebKit/Source/core/loader/EmptyClients.cpp

Index: third_party/WebKit/Source/core/loader/EmptyClients.cpp
diff --git a/third_party/WebKit/Source/core/loader/EmptyClients.cpp b/third_party/WebKit/Source/core/loader/EmptyClients.cpp
index ec637fc65856cde53d60c4bda9b6d30d885b2e85..003ff950d592409eae75657130a2ba9e8b833ffe 100644
--- a/third_party/WebKit/Source/core/loader/EmptyClients.cpp
+++ b/third_party/WebKit/Source/core/loader/EmptyClients.cpp
@@ -76,6 +76,7 @@ class EmptyFrameScheduler : public WebFrameScheduler {
   RefPtr<WebTaskRunner> TimerTaskRunner() override;
   RefPtr<WebTaskRunner> UnthrottledTaskRunner() override;
   RefPtr<WebTaskRunner> SuspendableTaskRunner() override;
+  RefPtr<WebTaskRunner> UnthrottledButBlockableTaskRunner() override;
 };
 
 RefPtr<WebTaskRunner> EmptyFrameScheduler::LoadingTaskRunner() {
@@ -94,6 +95,10 @@ RefPtr<WebTaskRunner> EmptyFrameScheduler::SuspendableTaskRunner() {
   return Platform::Current()->MainThread()->GetWebTaskRunner();
 }
 
+RefPtr<WebTaskRunner> EmptyFrameScheduler::UnthrottledButBlockableTaskRunner() {
+  return Platform::Current()->MainThread()->GetWebTaskRunner();
+}
+
 PopupMenu* EmptyChromeClient::OpenPopupMenu(LocalFrame&, HTMLSelectElement&) {
   return new EmptyPopupMenu();
 }