Add CHECKs to make sure ThreadableLoader has not been created multiple times

third_party/WebKit/Source/core/workers/WorkerScriptLoader.cpp

Index: third_party/WebKit/Source/core/workers/WorkerScriptLoader.cpp
diff --git a/third_party/WebKit/Source/core/workers/WorkerScriptLoader.cpp b/third_party/WebKit/Source/core/workers/WorkerScriptLoader.cpp
index c0d1b0762f7b094daf11662bd57504ee22ffffa0..64d6f9bce315726c13907925cdb2f31f19dcc64b 100644
--- a/third_party/WebKit/Source/core/workers/WorkerScriptLoader.cpp
+++ b/third_party/WebKit/Source/core/workers/WorkerScriptLoader.cpp
@@ -78,6 +78,8 @@ void WorkerScriptLoader::loadSynchronously(
   ResourceLoaderOptions resourceLoaderOptions;
   resourceLoaderOptions.allowCredentials = AllowStoredCredentials;
 
+  // TODO(yhirano): Remove this CHECK once https://crbug.com/667254 is fixed.
+  CHECK(!m_threadableLoader);
   WorkerThreadableLoader::loadResourceSynchronously(
       toWorkerGlobalScope(executionContext), request, *this, options,
       resourceLoaderOptions);
@@ -108,6 +110,8 @@ void WorkerScriptLoader::loadAsynchronously(
   // (E.g. see crbug.com/524694 for why we can't easily remove this protect)
   RefPtr<WorkerScriptLoader> protect(this);
   m_needToCancel = true;
+  // TODO(yhirano): Remove this CHECK once https://crbug.com/667254 is fixed.
+  CHECK(!m_threadableLoader);
   m_threadableLoader = ThreadableLoader::create(executionContext, this, options,
                                                 resourceLoaderOptions);
   m_threadableLoader->start(request);