Added UseCounter for XML external DTD.

BUG=367689

Review URL: https://codereview.chromium.org/552673002

git-svn-id: svn://svn.chromium.org/blink/trunk@181602 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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

@@ -497,6 +497,8 @@ public:
         MediaStreamEnded = 526,
         MixedContentPrivateIPInPublicWebsitePassive = 527,
         MixedContentPrivateIPInPublicWebsiteActive = 528,
+        XMLExternalResourceLoad = 529,
+
         // 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/parser/XMLDocumentParser.cpp

@@ -657,6 +657,8 @@ static void* openFunc(const char* uri)
     if (!shouldAllowExternalLoad(finalURL))
         return &globalDescriptor;
 
+    UseCounter::count(XMLDocumentParserScope::currentFetcher->document(), UseCounter::XMLExternalResourceLoad);
+
     return new SharedBufferReader(data);
 }