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

third_party/WebKit/Source/core/dom/TaskRunnerHelper.cpp

 // Copyright 2016 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 "core/dom/TaskRunnerHelper.h"
 
 #include "core/dom/Document.h"
 #include "core/dom/ExecutionContext.h"
 #include "core/frame/LocalFrame.h"
 #include "core/workers/MainThreadWorkletGlobalScope.h"
@@ skipping 35 matching lines @@
     case TaskType::kMicrotask:
     case TaskType::kPostedMessage:
     case TaskType::kUnshippedPortMessage:
     case TaskType::kFileReading:
     case TaskType::kPresentation:
     case TaskType::kSensor:
     case TaskType::kPerformanceTimeline:
     case TaskType::kWebGL:
     case TaskType::kUnspecedTimer:
     case TaskType::kMiscPlatformAPI:
+      // TODO(altimin): Move all these tasks to suspendable or unthrottled
+      // task runner.
+      return frame
+                 ? frame->FrameScheduler()->UnthrottledButBlockableTaskRunner()
+                 : Platform::Current()->CurrentThread()->GetWebTaskRunner();
     case TaskType::kUnthrottled:
       return frame ? frame->FrameScheduler()->UnthrottledTaskRunner()
                    : Platform::Current()->CurrentThread()->GetWebTaskRunner();
   }
   NOTREACHED();
   return nullptr;
 }
 
 RefPtr<WebTaskRunner> TaskRunnerHelper::Get(TaskType type, Document* document) {
   return Get(type, document ? document->GetFrame() : nullptr);
@@ skipping 60 matching lines @@
       // TODO(nhiroki): Identify which tasks can be throttled / suspendable and
       // move them into other task runners. See also comments in
       // Get(LocalFrame). (https://crbug.com/670534)
       return worker_thread->GetGlobalScopeScheduler()->UnthrottledTaskRunner();
   }
   NOTREACHED();
   return nullptr;
 }
 
 }  // namespace blink