[XMLHttpRequest] Stop throwing for network error in async mode

LayoutTests/fast/files/apply-blob-url-to-xhr-expected.txt

Index: LayoutTests/fast/files/apply-blob-url-to-xhr-expected.txt
diff --git a/LayoutTests/fast/files/apply-blob-url-to-xhr-expected.txt b/LayoutTests/fast/files/apply-blob-url-to-xhr-expected.txt
index 28eb637ebeb74fbc1b0eba2133c652fefba213a3..4637b6dc4dde8bded7e9778e8cfe8106ad032923 100644
--- a/LayoutTests/fast/files/apply-blob-url-to-xhr-expected.txt
+++ b/LayoutTests/fast/files/apply-blob-url-to-xhr-expected.txt
@@ -1,11 +1,19 @@
 CONSOLE WARNING: Synchronous XMLHttpRequest on the main thread is deprecated because of its detrimental effects to the end user's experience. For more help, check http://xhr.spec.whatwg.org/.
 
-Test that XMLHttpRequest GET succeeds.
+Test that sync XMLHttpRequest GET succeeds.
 Status: 200
 Response: Hello
-Test that XMLHttpRequest POST fails.
-Received exception, code: 19, name: NetworkError, message: Failed to execute 'send' on 'XMLHttpRequest': 'GET' is the only method allowed for 'blob:' URLs.
-Test that XMLHttpRequest GET fails after the blob URL is revoked.
+Test that sync XMLHttpRequest POST fails.
+Received exception, code: 19, name: NetworkError, message: Failed to execute 'send' on 'XMLHttpRequest': Failed to load 'blob:file%3A///UUID': 'GET' is the only method allowed for 'blob:' URLs.
+Test that sync XMLHttpRequest GET fails after the blob URL is revoked.
+Status: 404
+Response: 
+Test that async XMLHttpRequest GET succeeds.
+Status: 200
+Response: Hello
+Test that async XMLHttpRequest POST fails.
+Error event is dispatched
+Test that async XMLHttpRequest GET fails after the blob URL is revoked.
 Status: 404
 Response: 
 DONE