Deprecate support for xhr.withCredentials for synchronous requests

Source/core/xml/XMLHttpRequest.cpp

Index: Source/core/xml/XMLHttpRequest.cpp
diff --git a/Source/core/xml/XMLHttpRequest.cpp b/Source/core/xml/XMLHttpRequest.cpp
index 1d1c58056583a774c5898b0b6359af2fd9a9258f..77fba6242f36756aa4b12327736e54949ed0660e 100644
--- a/Source/core/xml/XMLHttpRequest.cpp
+++ b/Source/core/xml/XMLHttpRequest.cpp
@@ -487,6 +487,11 @@ void XMLHttpRequest::setWithCredentials(bool value, ExceptionState& exceptionSta
         return;
     }
 
+    // FIXME: According to XMLHttpRequest Level 2 we should throw InvalidAccessError exception here.
+    // However for time being only print warning message to warn web developers.
+    if (!m_async)
+        UseCounter::countDeprecation(executionContext(), UseCounter::SyncXHRWithCredentials);
+
     m_includeCredentials = value;
 }