Add use counters for elements used in Shadow DOM

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

Index: third_party/WebKit/Source/core/frame/UseCounter.h
diff --git a/third_party/WebKit/Source/core/frame/UseCounter.h b/third_party/WebKit/Source/core/frame/UseCounter.h
index c573f544652eb950344b8765ae795f62278cf2fa..23759e760db2610a49132c68d534b9dda1c94cf6 100644
--- a/third_party/WebKit/Source/core/frame/UseCounter.h
+++ b/third_party/WebKit/Source/core/frame/UseCounter.h
@@ -1513,6 +1513,9 @@ class CORE_EXPORT UseCounter {
     WebBluetoothRemoteServerGetPrimaryServices = 1893,
     WebBluetoothRemoteServiceGetCharacteristic = 1894,
     WebBluetoothRemoteServiceGetCharacteristics = 1895,
+    HTMLContentElement = 1896,
+    HTMLShadowElement = 1897,
+    HTMLSlotElement = 1898,
 
     // Add new features immediately above this line. Don't change assigned
     // numbers of any item, and don't reuse removed slots.