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..78b24ae89041828aff3ca2c2bd0cdf1af8a375b8 100644
--- a/Source/core/loader/ThreadableLoader.h
+++ b/Source/core/loader/ThreadableLoader.h
@@ -125,7 +125,9 @@ namespace blink {
         // 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&);
+        static PassRefPtr<ThreadableLoader> create(ExecutionContext&, ThreadableLoaderClient*, const ThreadableLoaderOptions&, const ResourceLoaderOptions&);

[hiroshige, 2015/07/28 11:35:37]

From the CL description:
Then should we move the ThreadableLoaderClient* argument to start() to make
explcit that the client's callback is not called from the constructor?

[hiroshige, 2015/07/28 11:35:37]

What is the reason for moving ResourceRequest& argument to start()? Please
describe it in the CL description.

[tyoshino (SeeGerritForStatus), 2015/07/28 12:21:50]

ResourceRequest is not stored in a member variable in DocumentThreadableLoader.
Passing it on construction requires adding a new variable that is used only
between create() and start(). I wanted to avoid that.

[tyoshino (SeeGerritForStatus), 2015/07/28 12:21:51]

Ah, I see. It also works! Maybe we should move almost everything.

[tyoshino (SeeGerritForStatus), 2015/07/28 12:36:54]

Hmm, but this needs much work. Can I postpone it?

[tyoshino (SeeGerritForStatus), 2015/07/28 12:36:55]

Updated the CL description.

[hiroshige, 2015/07/30 12:07:21]

Yes.
Then please add a comment stating that ThreadableLoaderClient* methods are not
called in create(), but can be called synchronously in start().

[tyoshino (SeeGerritForStatus), 2015/07/31 08:00:42]

Done.

+
+        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