Introduce ThreadableLoadingContext: make threaded loading code one step away from Document

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

Index: third_party/WebKit/Source/core/loader/ThreadableLoader.cpp
diff --git a/third_party/WebKit/Source/core/loader/ThreadableLoader.cpp b/third_party/WebKit/Source/core/loader/ThreadableLoader.cpp
index 11cedc543327d4ff784f6e7032b58911b7423233..63cefa8db4d2e91d0e78283b3dec8718f7360008 100644
--- a/third_party/WebKit/Source/core/loader/ThreadableLoader.cpp
+++ b/third_party/WebKit/Source/core/loader/ThreadableLoader.cpp
@@ -33,6 +33,7 @@
 #include "core/dom/Document.h"
 #include "core/dom/ExecutionContext.h"
 #include "core/loader/DocumentThreadableLoader.h"
+#include "core/loader/ThreadableLoadingContext.h"
 #include "core/loader/WorkerThreadableLoader.h"
 #include "core/workers/WorkerGlobalScope.h"
 
@@ -50,8 +51,9 @@ ThreadableLoader* ThreadableLoader::create(
                                           options, resourceLoaderOptions);
   }
 
-  return DocumentThreadableLoader::create(toDocument(context), client, options,
-                                          resourceLoaderOptions);
+  return DocumentThreadableLoader::create(
+      *ThreadableLoadingContext::create(*toDocument(&context)), client, options,
+      resourceLoaderOptions);
 }
 
 void ThreadableLoader::loadResourceSynchronously(