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

Source/modules/filesystem/InspectorFileSystemAgent.cpp

Index: Source/modules/filesystem/InspectorFileSystemAgent.cpp
diff --git a/Source/modules/filesystem/InspectorFileSystemAgent.cpp b/Source/modules/filesystem/InspectorFileSystemAgent.cpp
index aaef46227822a5a7a7eecd0c3b4d9889f4dd7df5..e90cc5cae88dbe37ff31c7b69030fd7cb76e0ae8 100644
--- a/Source/modules/filesystem/InspectorFileSystemAgent.cpp
+++ b/Source/modules/filesystem/InspectorFileSystemAgent.cpp
@@ -32,6 +32,7 @@
 #include "modules/filesystem/InspectorFileSystemAgent.h"
 
 #include "bindings/core/v8/ExceptionStatePlaceholder.h"
+#include "bindings/core/v8/UnionTypesCore.h"
 #include "core/dom/DOMArrayBuffer.h"
 #include "core/dom/DOMImplementation.h"
 #include "core/dom/Document.h"
@@ -482,7 +483,9 @@ bool FileContentRequest::didGetFile(File* file)
 
 void FileContentRequest::didRead()
 {
-    RefPtr<DOMArrayBuffer> buffer = m_reader->arrayBufferResult();
+    StringOrArrayBuffer resultAttribute;
+    m_reader->result(resultAttribute);
+    RefPtr<DOMArrayBuffer> buffer = resultAttribute.getAsArrayBuffer();
 
     if (!m_readAsText) {
         String result = base64Encode(static_cast<char*>(buffer->data()), buffer->byteLength());