Revert of DatabaseBackend objects should be destructed in the originator thread

Source/modules/webdatabase/DatabaseThread.cpp

Index: Source/modules/webdatabase/DatabaseThread.cpp
diff --git a/Source/modules/webdatabase/DatabaseThread.cpp b/Source/modules/webdatabase/DatabaseThread.cpp
index 9c83d901cffedbf0c7f8d8049805c9a9d61b4afd..4f7ceabd5e1ce719699417f8a268b6e5ba62fbc7 100644
--- a/Source/modules/webdatabase/DatabaseThread.cpp
+++ b/Source/modules/webdatabase/DatabaseThread.cpp
@@ -48,8 +48,6 @@
 
 DatabaseThread::~DatabaseThread()
 {
-    ASSERT(m_thread);
-    ASSERT(!isDatabaseThread());
     bool terminationRequested;
     {
         MutexLocker lock(m_terminationRequestedMutex);
@@ -98,8 +96,11 @@
     // Close the databases that we ran transactions on. This ensures that if any transactions are still open, they are rolled back and we don't leave the database in an
     // inconsistent or locked state.
     if (m_openDatabaseSet.size() > 0) {
-        DatabaseSet::iterator end = m_openDatabaseSet.end();
-        for (DatabaseSet::iterator it = m_openDatabaseSet.begin(); it != end; ++it)
+        // As the call to close will modify the original set, we must take a copy to iterate over.
+        DatabaseSet openSetCopy;
+        openSetCopy.swap(m_openDatabaseSet);
+        DatabaseSet::iterator end = openSetCopy.end();
+        for (DatabaseSet::iterator it = openSetCopy.begin(); it != end; ++it)
             (*it).get()->close();
     }
 
@@ -121,9 +122,17 @@
     MutexLocker lock(m_terminationRequestedMutex);
 #endif
     ASSERT(isDatabaseThread());
-    ASSERT_UNUSED(database, database);
+    ASSERT(database);
     ASSERT(m_terminationRequested || m_openDatabaseSet.contains(database));
-    // We'll clear m_openDatabaseSet in the destructor.
+    m_openDatabaseSet.remove(database);
+}
+
+bool DatabaseThread::isDatabaseOpen(DatabaseBackend* database)
+{
+    ASSERT(isDatabaseThread());
+    ASSERT(database);
+    MutexLocker lock(m_terminationRequestedMutex);
+    return !m_terminationRequested && m_openDatabaseSet.contains(database);
 }
 
 void DatabaseThread::scheduleTask(PassOwnPtr<DatabaseTask> task)