Add use counters to determine the fate of DOMStringList

Source/modules/indexeddb/IDBDatabase.cpp

Index: Source/modules/indexeddb/IDBDatabase.cpp
diff --git a/Source/modules/indexeddb/IDBDatabase.cpp b/Source/modules/indexeddb/IDBDatabase.cpp
index d365d959afae1069d25fc9ad5a2c98841e6b0420..a5bec351800c1de5e58681149b2d6e4c33bbc0ab 100644
--- a/Source/modules/indexeddb/IDBDatabase.cpp
+++ b/Source/modules/indexeddb/IDBDatabase.cpp
@@ -33,6 +33,7 @@
 #include "bindings/modules/v8/V8BindingForModules.h"
 #include "core/dom/ExecutionContext.h"
 #include "core/events/EventQueue.h"
+#include "core/frame/UseCounter.h"
 #include "core/inspector/ScriptCallStack.h"
 #include "modules/indexeddb/IDBAny.h"
 #include "modules/indexeddb/IDBEventDispatcher.h"
@@ -277,6 +278,7 @@ IDBTransaction* IDBDatabase::transaction(ScriptState* scriptState, const StringO
         for (const String& name : storeNames.getAsStringSequence())
             scope.add(name);
     } else if (storeNames.isDOMStringList()) {
+        UseCounter::count(executionContext(), UseCounter::IDBDatabaseTransactionStoreNamesIsDOMStringList);

[jsbell, 2015/06/05 18:12:17]

This won't tell us anything useful. Given that user code can't mint a
DOMStringList, this case is only practically exercised by:

db.transaction(db.objectStoreNames);

... where objectStoreNames yields a DOMStringList, so we'd already be counting
that usage, and if we change it to return an Array it would continue to work.

But no objection, since the data won't hurt.

[philipj_slow, 2015/06/05 18:19:22]

You're right, that sounds pretty useless, so I'll remove this. If all of the
ways of getting a DOMStringList go away, so can this.

         const Vector<String>& list = *storeNames.getAsDOMStringList();
         for (const String& name : list)
             scope.add(name);