Rename DatabaseTaskSynchronizer to TaskSynchronizer and move it to platform/

Source/modules/webdatabase/Database.cpp

Index: Source/modules/webdatabase/Database.cpp
diff --git a/Source/modules/webdatabase/Database.cpp b/Source/modules/webdatabase/Database.cpp
index 2a55f3d859969c521302c469d57264f3ce0cfe0f..ca552cbdd24501db880a8f36a465ede3b9446859 100644
--- a/Source/modules/webdatabase/Database.cpp
+++ b/Source/modules/webdatabase/Database.cpp
@@ -215,7 +215,7 @@ Vector<String> Database::tableNames()
     // FIXME: Not using isolatedCopy on these strings looks ok since threads take strict turns
     // in dealing with them. However, if the code changes, this may not be true anymore.
     Vector<String> result;
-    DatabaseTaskSynchronizer synchronizer;
+    TaskSynchronizer synchronizer;
     if (!databaseContext()->databaseThread() || databaseContext()->databaseThread()->terminationRequested(&synchronizer))
         return result;