Split the constructor of ThreadableLoader into two methods (ctor and start())

Source/core/loader/ThreadableLoader.h

Index: Source/core/loader/ThreadableLoader.h
diff --git a/Source/core/loader/ThreadableLoader.h b/Source/core/loader/ThreadableLoader.h
index dc8f3ef02e9da2a4776cb0e5e284f45cf2d0d75c..443ce0ecdda06eb462352fafa686c811706d48ae 100644
--- a/Source/core/loader/ThreadableLoader.h
+++ b/Source/core/loader/ThreadableLoader.h
@@ -124,8 +124,15 @@ namespace blink {
         // ResourceLoaderOptions argument will be passed to the FetchRequest
         // that this ThreadableLoader creates. It can be altered e.g. when
         // redirect happens.
+
         static void loadResourceSynchronously(ExecutionContext&, const ResourceRequest&, ThreadableLoaderClient&, const ThreadableLoaderOptions&, const ResourceLoaderOptions&);
-        static PassRefPtr<ThreadableLoader> create(ExecutionContext&, ThreadableLoaderClient*, const ResourceRequest&, const ThreadableLoaderOptions&, const ResourceLoaderOptions&);
+        // create() must always followed by start() call.

[hiroshige, 2015/08/10 15:00:05]

Please mention that create() never returns null.

[tyoshino (SeeGerritForStatus), 2016/01/29 12:36:52]

Done.

[tyoshino (SeeGerritForStatus), 2016/01/29 12:37:56]

This reply had to be published before.

+        // |ThreadableLoaderClient| methods are never called before start() call.
+        static PassRefPtr<ThreadableLoader> create(ExecutionContext&, ThreadableLoaderClient*, const ThreadableLoaderOptions&, const ResourceLoaderOptions&);
+
+        // The methods on the |ThreadableLoaderClient| may be called
+        // synchronous to start() call.
+        virtual void start(const ResourceRequest&) = 0;
 
         // A ThreadableLoader may have a timeout specified. It is possible, in some cases, for
         // the timeout to be overridden after the request is sent (for example, XMLHttpRequests