[Fetch API] Send request body as a FormData.

Source/modules/fetch/Request.h

Index: Source/modules/fetch/Request.h
diff --git a/Source/modules/fetch/Request.h b/Source/modules/fetch/Request.h
index de52e6be3e2469c90b9683c57e531fcafce6f62a..410e21106396cc25a69674a8c1dba9c30dfdf1b5 100644
--- a/Source/modules/fetch/Request.h
+++ b/Source/modules/fetch/Request.h
@@ -68,7 +68,7 @@ private:
     Request(ExecutionContext*, FetchRequestData*, Headers*);
 
     const FetchRequestData* request() const { return m_request; }
-    static Request* createRequestWithRequestOrString(ScriptState*, Request*, const String&, const RequestInit&, ExceptionState&);

[hiroshige, 2015/08/17 08:46:02]

nit optional: I think removing |const| here is to allow
RequestInit::body.release(), but passing non-const reference looks like it is
variable for output.
Using PassOwnPtr<RequestInit> might be clearer.
But it's optional because this is an internal function...

another nit optional: we can remove declaration of 
createRequestWithRequestOrString() here and move
createCopyOfFetchRequestDataForFetch() and createRequestWithRequestOrString()
into an anonymous namespace in Request.cpp.

[yhirano, 2015/08/18 09:12:39]

RequestInit is marked as STACK_ALLOCATED due to an oilpan reason and I would
like to keep it.
The function uses many private methods / members, so I would keep the
declaration.

[hiroshige, 2015/08/18 09:36:53]

Acknowledged.

+    static Request* createRequestWithRequestOrString(ScriptState*, Request*, const String&, RequestInit&, ExceptionState&);
 
     String mimeType() const override;