Add a deprecation message for multiple shadow roots.

Source/core/dom/shadow/ElementShadow.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Neither the name of Google Inc. nor the names of its
@@ skipping 131 matching lines @@
     removeDetachedShadowRoots();
 #endif
 }
 
 ShadowRoot& ElementShadow::addShadowRoot(Element& shadowHost, ShadowRoot::ShadowRootType type)
 {
     EventDispatchForbiddenScope assertNoEventDispatch;
     ScriptForbiddenScope forbidScript;
 
     if (type == ShadowRoot::OpenShadowRoot) {
-        if (!youngestShadowRoot() || youngestShadowRoot()->type() == ShadowRoot::UserAgentShadowRoot)
+        if (!youngestShadowRoot()) {
             shadowHost.willAddFirstOpenShadowRoot();
-        else
-            UseCounter::count(shadowHost.document(), UseCounter::ElementCreateShadowRootMultiple);
+        } else if (youngestShadowRoot()->type() == ShadowRoot::UserAgentShadowRoot) {
+            shadowHost.willAddFirstOpenShadowRoot();
+            UseCounter::countDeprecation(shadowHost.document(), UseCounter::ElementCreateShadowRootMultipleWithUserAgentShadowRoot);
+        } else {
+            UseCounter::countDeprecation(shadowHost.document(), UseCounter::ElementCreateShadowRootMultiple);
+        }
     }
 
     for (ShadowRoot* root = youngestShadowRoot(); root; root = root->olderShadowRoot())
         root->lazyReattachIfAttached();
 
     RefPtrWillBeRawPtr<ShadowRoot> shadowRoot = ShadowRoot::create(shadowHost.document(), type);
     shadowRoot->setParentOrShadowHostNode(&shadowHost);
     shadowRoot->setParentTreeScope(shadowHost.treeScope());
     m_shadowRoots.push(shadowRoot.get());
     setNeedsDistributionRecalc();
@@ skipping 210 matching lines @@
     visitor->trace(m_nodeToInsertionPoints);
     visitor->trace(m_selectFeatures);
     // Shadow roots are linked with previous and next pointers which are traced.
     // It is therefore enough to trace one of the shadow roots here and the
     // rest will be traced from there.
     visitor->trace(m_shadowRoots.head());
 #endif
 }
 
 } // namespace