Add some <base> metrics to guide experimentation.

third_party/WebKit/Source/core/dom/Document.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2011, 2012 Apple Inc. All
  * rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved.
  * (http://www.torchmobile.com/)
  * Copyright (C) 2008, 2009, 2011, 2012 Google Inc. All rights reserved.
@@ skipping 3269 matching lines @@
       anchor.invalidateCachedVisitedLinkHash();
   }
 }
 
 void Document::setBaseURLOverride(const KURL& url) {
   m_baseURLOverride = url;
   updateBaseURL();
 }
 
 void Document::processBaseElement() {
+  UseCounter::count(*this, UseCounter::BaseElement);
+
   // Find the first href attribute in a base element and the first target
   // attribute in a base element.
   const AtomicString* href = 0;
   const AtomicString* target = 0;
   for (HTMLBaseElement* base = Traversal<HTMLBaseElement>::firstWithin(*this);
        base && (!href || !target);
        base = Traversal<HTMLBaseElement>::next(*base)) {
     if (!href) {
       const AtomicString& value = base->fastGetAttribute(hrefAttr);
       if (!value.isNull())
         href = &value;
     }
     if (!target) {
       const AtomicString& value = base->fastGetAttribute(targetAttr);
       if (!value.isNull())
         target = &value;
     }
-    if (contentSecurityPolicy()->isActive())
+    if (contentSecurityPolicy()->isActive()) {
       UseCounter::count(*this,
                         UseCounter::ContentSecurityPolicyWithBaseElement);
+    }
   }
 
   // FIXME: Since this doesn't share code with completeURL it may not handle
   // encodings correctly.
   KURL baseElementURL;
   if (href) {
     String strippedHref = stripLeadingAndTrailingHTMLSpaces(*href);
     if (!strippedHref.isEmpty())
       baseElementURL = KURL(url(), strippedHref);
   }
+
+  if (!baseElementURL.isEmpty()) {
+    if (baseElementURL.protocolIsData())
+      UseCounter::count(*this, UseCounter::BaseWithDataHref);
+    if (!this->getSecurityOrigin()->canRequest(baseElementURL))
+      UseCounter::count(*this, UseCounter::BaseWithCrossOriginHref);
+  }
+
   if (m_baseElementURL != baseElementURL &&
       contentSecurityPolicy()->allowBaseURI(baseElementURL)) {
     m_baseElementURL = baseElementURL;
     updateBaseURL();
   }
 
-  m_baseTarget = target ? *target : nullAtom;
+  if (target) {
+    if (target->contains('\n') || target->contains('\r'))
+      UseCounter::count(*this, UseCounter::BaseWithNewlinesInTarget);
+    if (target->contains('<'))
+      UseCounter::count(*this, UseCounter::BaseWithOpenBracketInTarget);
+    m_baseTarget = *target;
+  } else {
+    m_baseTarget = nullAtom;
+  }
 }
 
 String Document::userAgent() const {
   return frame() ? frame()->loader().userAgent() : String();
 }
 
 void Document::disableEval(const String& errorMessage) {
   if (!frame())
     return;
 
@@ skipping 3138 matching lines @@
 }
 
 void showLiveDocumentInstances() {
   WeakDocumentSet& set = liveDocumentSet();
   fprintf(stderr, "There are %u documents currently alive:\n", set.size());
   for (Document* document : set)
     fprintf(stderr, "- Document %p URL: %s\n", document,
             document->url().getString().utf8().data());
 }
 #endif