I see the following test failure on Windows with the updated webkit from JDK-8156698:

java.io.IOException: Error deleting [foo\localstorage\file__0.localstorage]
at test.javafx.scene.web.UserDataDirectoryTest.deleteRecursively(UserDataDirectoryTest.java:572)
at test.javafx.scene.web.UserDataDirectoryTest.deleteRecursively(UserDataDirectoryTest.java:568)
at test.javafx.scene.web.UserDataDirectoryTest.deleteRecursively(UserDataDirectoryTest.java:568)
at test.javafx.scene.web.UserDataDirectoryTest.afterClass(UserDataDirectoryTest.java:103)

The following log messages are written to stderr:

onError: WebErrorEvent [source = javafx.scene.web.WebEngine@d51fdb, eventType = USER_DATA_DIRECTORY_IO_ERROR, message = "An I/O error occurred while setting up user data directory [qux]", exception = java.nio.file.FileAlreadyExistsException: modules\web\qux]
onError: WebErrorEvent [source = javafx.scene.web.WebEngine@1e8fb8d, eventType = USER_DATA_DIRECTORY_ALREADY_IN_USE, message = "User data directory [baz] is already in use", exception = javafx.scene.web.DirectoryLock$DirectoryAlreadyInUseException: modules\web\baz]
onError: WebErrorEvent [source = javafx.scene.web.WebEngine@af62ee, eventType = USER_DATA_DIRECTORY_SECURITY_ERROR, message = "A security error occurred while setting up user data directory [foo]", exception = java.security.AccessControlException: access denied ("java.io.FilePermission" "modules\web\foo" "write")]