[bindings] Make sure v8::Isolate is being passed to toXXX() conversion routines as argument.

Source/modules/fetch/RequestInit.cpp

Index: Source/modules/fetch/RequestInit.cpp
diff --git a/Source/modules/fetch/RequestInit.cpp b/Source/modules/fetch/RequestInit.cpp
index 83bd81578fef8a0b6860e6ae949fa42906c30c4e..df34d4aa04bf54468da06c457a30bc6af2d3a771 100644
--- a/Source/modules/fetch/RequestInit.cpp
+++ b/Source/modules/fetch/RequestInit.cpp
@@ -77,7 +77,7 @@ RequestInit::RequestInit(ExecutionContext* context, const Dictionary& options, E
         }
         blobData->setContentType(AtomicString("multipart/form-data; boundary=", AtomicString::ConstructFromLiteral) + httpBody->boundary().data());
     } else if (body->IsString()) {
-        String stringValue(toUSVString(body, exceptionState));
+        String stringValue(toUSVString(isolate, body, exceptionState));
         blobData->appendText(stringValue, false);
         blobData->setContentType("text/plain;charset=UTF-8");
     } else {