FileReader.result attribute should use IDL union types to avoid using custom binding.

Source/core/fileapi/FileReader.cpp

Index: Source/core/fileapi/FileReader.cpp
diff --git a/Source/core/fileapi/FileReader.cpp b/Source/core/fileapi/FileReader.cpp
index d55d1b99a2861ac67792fc9f9090a62f60f3c354..e3db51ff240dbf58eb272fed69d4894c92e17ac5 100644
--- a/Source/core/fileapi/FileReader.cpp
+++ b/Source/core/fileapi/FileReader.cpp
@@ -32,6 +32,7 @@
 #include "core/fileapi/FileReader.h"
 
 #include "bindings/core/v8/ExceptionState.h"
+#include "bindings/core/v8/UnionTypesCore.h"
 #include "core/dom/CrossThreadTask.h"
 #include "core/dom/DOMArrayBuffer.h"
 #include "core/dom/Document.h"
@@ -364,6 +365,17 @@ void FileReader::doAbort()
     ThrottlingController::finishReader(executionContext(), this, finalStep);
 }
 
+void FileReader::result(StringOrArrayBuffer& resultAttribute) const
+{
+    if (!m_loader || m_error)
+        return;
+
+    if (m_readType == FileReaderLoader::ReadAsArrayBuffer)
+        resultAttribute.setArrayBuffer(m_loader->arrayBufferResult());
+    else
+        resultAttribute.setString(m_loader->stringResult());
+}
+
 void FileReader::terminate()
 {
     if (m_loader) {
@@ -456,20 +468,6 @@ void FileReader::fireEvent(const AtomicString& type)
     InspectorInstrumentation::traceAsyncCallbackCompleted(cookie);
 }
 
-PassRefPtr<DOMArrayBuffer> FileReader::arrayBufferResult() const
-{
-    if (!m_loader || m_error)
-        return nullptr;
-    return m_loader->arrayBufferResult();
-}
-
-String FileReader::stringResult()
-{
-    if (!m_loader || m_error)
-        return String();
-    return m_loader->stringResult();
-}
-
 void FileReader::trace(Visitor* visitor)
 {
     visitor->trace(m_error);