Add UseCounter for multiple createShadowRoot() for deprecation

Source/core/dom/shadow/ElementShadow.cpp

Index: Source/core/dom/shadow/ElementShadow.cpp
diff --git a/Source/core/dom/shadow/ElementShadow.cpp b/Source/core/dom/shadow/ElementShadow.cpp
index ad449159c82d820e2b629b0609037e6acb4b7aa4..9276974aa453970fc9e0959331060577a6012e98 100644
--- a/Source/core/dom/shadow/ElementShadow.cpp
+++ b/Source/core/dom/shadow/ElementShadow.cpp
@@ -31,6 +31,7 @@
 #include "core/dom/ElementTraversal.h"
 #include "core/dom/NodeTraversal.h"
 #include "core/dom/shadow/DistributedNodes.h"
+#include "core/frame/UseCounter.h"
 #include "core/html/HTMLContentElement.h"
 #include "core/html/HTMLShadowElement.h"
 #include "core/inspector/InspectorInstrumentation.h"
@@ -147,8 +148,12 @@ ShadowRoot& ElementShadow::addShadowRoot(Element& shadowHost, ShadowRoot::Shadow
     EventDispatchForbiddenScope assertNoEventDispatch;
     ScriptForbiddenScope forbidScript;
 
-    if (type == ShadowRoot::OpenShadowRoot && (!youngestShadowRoot() || youngestShadowRoot()->type() == ShadowRoot::UserAgentShadowRoot))
-        shadowHost.willAddFirstOpenShadowRoot();
+    if (type == ShadowRoot::OpenShadowRoot) {
+        if (!youngestShadowRoot() || youngestShadowRoot()->type() == ShadowRoot::UserAgentShadowRoot)
+            shadowHost.willAddFirstOpenShadowRoot();
+        else
+            UseCounter::count(shadowHost.document(), UseCounter::ElementCreateShadowRootMultiple);
+    }
 
     for (ShadowRoot* root = youngestShadowRoot(); root; root = root->olderShadowRoot())
         root->lazyReattachIfAttached();