[Fetch API] Send request body as a FormData.

Source/modules/fetch/BodyStreamBuffer.h

Index: Source/modules/fetch/BodyStreamBuffer.h
diff --git a/Source/modules/fetch/BodyStreamBuffer.h b/Source/modules/fetch/BodyStreamBuffer.h
index d3790d3eedc4be102acd7a64c2a566b0db28e2af..2458798caff817c2c7a7c931ed0601205aae67b5 100644
--- a/Source/modules/fetch/BodyStreamBuffer.h
+++ b/Source/modules/fetch/BodyStreamBuffer.h
@@ -20,6 +20,7 @@
 namespace blink {
 
 class ExecutionContext;
+class FormData;
 
 // A BodyStreamBuffer constructed with a null handle is said to have null body.
 // One can observe if a buffer has null body by calling |hasBody| function.
@@ -37,6 +38,7 @@ public:
 
     // Callable only when not locked.
     PassRefPtr<BlobDataHandle> drainAsBlobDataHandle(FetchDataConsumerHandle::Reader::BlobSizePolicy);
+    PassRefPtr<FormData> drainAsFormData();
 
     // Callable only when not locked. Returns a non-null handle even when
     // having null body.