Revert of Pass per-frame task runners to Workers (when possible)

third_party/WebKit/Source/web/WebSharedWorkerImpl.cpp

Index: third_party/WebKit/Source/web/WebSharedWorkerImpl.cpp
diff --git a/third_party/WebKit/Source/web/WebSharedWorkerImpl.cpp b/third_party/WebKit/Source/web/WebSharedWorkerImpl.cpp
index f799c5b2739c975a22c5b9e31d99ff5d4fd4f5af..f397512a62f5b02edc8652cf706fb7325899310a 100644
--- a/third_party/WebKit/Source/web/WebSharedWorkerImpl.cpp
+++ b/third_party/WebKit/Source/web/WebSharedWorkerImpl.cpp
@@ -39,7 +39,6 @@
 #include "core/loader/FrameLoadRequest.h"
 #include "core/loader/FrameLoader.h"
 #include "core/page/Page.h"
-#include "core/workers/ParentFrameTaskRunners.h"
 #include "core/workers/SharedWorkerGlobalScope.h"
 #include "core/workers/SharedWorkerThread.h"
 #include "core/workers/WorkerClients.h"
@@ -272,8 +271,6 @@ void WebSharedWorkerImpl::workerThreadTerminatedOnMainThread()
 
 void WebSharedWorkerImpl::postTaskToLoader(const WebTraceLocation& location, std::unique_ptr<ExecutionContextTask> task)
 {
-    // TODO(hiroshige,yuryu): Make this not use ExecutionContextTask and
-    // consider using m_mainThreadTaskRunners->getLoadingTaskRunner() instead.
     m_mainFrame->frame()->document()->postTask(location, std::move(task));
 }
 
@@ -354,13 +351,6 @@ void WebSharedWorkerImpl::onScriptLoaderFinished()
         m_mainScriptLoader->responseAddressSpace(),
         m_mainScriptLoader->originTrialTokens(),
         std::move(workerSettings));
-
-    // We have a dummy document here for loading but it doesn't really represent
-    // the document/frame of associated document(s) for this worker. Here we
-    // populate the task runners with null document not to confuse the frame
-    // scheduler (which will end up using the thread's default task runner).
-    m_mainThreadTaskRunners = ParentFrameTaskRunners::create(nullptr);
-
     m_loaderProxy = WorkerLoaderProxy::create(this);
     m_workerThread = SharedWorkerThread::create(m_name, m_loaderProxy, *this);
     InspectorInstrumentation::scriptImported(m_loadingDocument.get(), m_mainScriptLoader->identifier(), m_mainScriptLoader->script());