Add UseCounter for synchronous XMLHttpRequests

This patch adds a UseCounter for only synchronous XMLHttpRequests.
This will count exactly once per per page using sync XHR requests.

Review URL: https://codereview.chromium.org/337283003

git-svn-id: svn://svn.chromium.org/blink/trunk@176351 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/frame/UseCounter.h

@@ -462,6 +462,7 @@ public:
         EditingAppleTabSpanClass = 462,
         HTMLImportsAsyncAttribute = 463,
         FontFaceSetReady = 464,
+        XMLHttpRequestSynchronous = 465,
         // Add new features immediately above this line. Don't change assigned
         // numbers of any item, and don't reuse removed slots.
         // Also, run update_use_counter_feature_enum.py in chromium/src/tools/metrics/histograms/

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

@@ -35,6 +35,8 @@
 #include "core/fileapi/Blob.h"
 #include "core/fileapi/File.h"
 #include "core/fileapi/Stream.h"
+#include "core/frame/Settings.h"
+#include "core/frame/UseCounter.h"
 #include "core/frame/csp/ContentSecurityPolicy.h"
 #include "core/html/DOMFormData.h"
 #include "core/html/HTMLDocument.h"
@@ -42,7 +44,6 @@
 #include "core/inspector/InspectorInstrumentation.h"
 #include "core/inspector/InspectorTraceEvents.h"
 #include "core/loader/ThreadableLoader.h"
-#include "core/frame/Settings.h"
 #include "core/xml/XMLHttpRequestProgressEvent.h"
 #include "core/xml/XMLHttpRequestUpload.h"
 #include "platform/Logging.h"
@@ -572,6 +573,9 @@ void XMLHttpRequest::open(const AtomicString& method, const KURL& url, bool asyn
     }
 
     if (!async && executionContext()->isDocument()) {
+        // Use count for XHR synchronous requests.
+        UseCounter::count(document(), UseCounter::XMLHttpRequestSynchronous);
+
         if (document()->settings() && !document()->settings()->syncXHRInDocumentsEnabled()) {
             exceptionState.throwDOMException(InvalidAccessError, "Synchronous requests are disabled for this page.");
             return;