FontManager.fileCloser may cause memory leak in applets

FontManager creates fileCloser to be executed at shutdown.

In applet environment this may be triggered from the application context and then contextClassLoader will be refering to applet's classloader.
This prevents classes loaded by this classloader from being unloaded (and their static state!) until thread is disposed.

However, in plugin same VM is reused for other apps and shutdown hook may be not be called for long period of time.

For FX applet this may cause leak of 10-20Mb depending on what applet was run first.

Here is the example of reference chains from the memory dump:

System Class Reference :
--> class sun.font.FontManager (84 bytes) (static field fileCloser:)
--> java.lang.Thread@0x281c3f70 (104 bytes) (field contextClassLoader:)
--> sun.plugin2.applet.JNLP2ClassLoader@0x27f08078 (136 bytes) (field classes:)
--> java.util.Vector@0x27f1bd10 (24 bytes) (field elementData:)
--> [Ljava.lang.Object;@0x283241e0 (5128 bytes) (Element 200 of [Ljava.lang.Object;@0x283241e0:)
--> class reversi.Main (84 bytes) (static field $titleImage:)
--> javafx.scene.image.ImageView@0x2814a7c0 (466 bytes) (field $platformImage:)
--> java.awt.image.BufferedImage@0x27f9a208 (37 bytes) (field raster:)
--> sun.awt.image.IntegerInterleavedRaster@0x27f9acf8 (101 bytes) (field dataBuffer:)
--> java.awt.image.DataBufferInt@0x27f9bde8 (36 bytes)

System Class Reference :
--> class java.lang.ApplicationShutdownHooks (84 bytes) (static field hooks:)
--> java.util.IdentityHashMap@0x27f14ec8 (36 bytes) (field table:)
--> [Ljava.lang.Object;@0x27f35fa8 (264 bytes) (Element 18 of [Ljava.lang.Object;@0x27f35fa8:)
--> java.lang.Thread@0x281c3f70 (104 bytes) (field contextClassLoader:)
--> sun.plugin2.applet.JNLP2ClassLoader@0x27f08078 (136 bytes) (field classes:)
--> java.util.Vector@0x27f1bd10 (24 bytes) (field elementData:)
--> [Ljava.lang.Object;@0x283241e0 (5128 bytes) (Element 200 of [Ljava.lang.Object;@0x283241e0:)
--> class reversi.Main (84 bytes) (static field $titleImage:)
--> javafx.scene.image.ImageView@0x2814a7c0 (466 bytes) (field $platformImage:)
--> java.awt.image.BufferedImage@0x27f9a208 (37 bytes) (field raster:)
--> sun.awt.image.IntegerInterleavedRaster@0x27f9acf8 (101 bytes) (field dataBuffer:)
--> java.awt.image.DataBufferInt@0x27f9bde8 (36 bytes)