Measure how many pages are using cross-origin XHR with withCredentials set to true

third_party/WebKit/Source/core/xmlhttprequest/XMLHttpRequest.cpp

Index: third_party/WebKit/Source/core/xmlhttprequest/XMLHttpRequest.cpp
diff --git a/third_party/WebKit/Source/core/xmlhttprequest/XMLHttpRequest.cpp b/third_party/WebKit/Source/core/xmlhttprequest/XMLHttpRequest.cpp
index 9de6192b2f7700726df325ae75865767f1db9dab..c471322ed17093d06019072f6d83260ab28c94a5 100644
--- a/third_party/WebKit/Source/core/xmlhttprequest/XMLHttpRequest.cpp
+++ b/third_party/WebKit/Source/core/xmlhttprequest/XMLHttpRequest.cpp
@@ -874,6 +874,9 @@ void XMLHttpRequest::createRequest(PassRefPtr<EncodedFormData> httpBody, Excepti
 
     m_sameOriginRequest = getSecurityOrigin()->canRequestNoSuborigin(m_url);
 
+    if (!m_sameOriginRequest && m_includeCredentials)
+        UseCounter::count(&executionContext, UseCounter::XMLHttpRequestCrossOriginWithCredentials);
+
     // We also remember whether upload events should be allowed for this request in case the upload listeners are
     // added after the request is started.
     m_uploadEventsAllowed = m_sameOriginRequest || uploadEvents || !FetchUtils::isSimpleRequest(m_method, m_requestHeaders);