implement JNI methods needed by AWT

These include PushLocalFrame, PopLocalFrame, NewDirectByteBuffer,
GetDirectBufferAddress, and GetDirectBufferCapacity.

classpath/java/nio/FixedArrayByteBuffer.java

@@ -0,0 +1,58 @@
+/* Copyright (c) 2008-2012, Avian Contributors
+
+   Permission to use, copy, modify, and/or distribute this software
+   for any purpose with or without fee is hereby granted, provided
+   that the above copyright notice and this permission notice appear
+   in all copies.
+
+   There is NO WARRANTY for this software.  See license.txt for
+   details. */
+
+package java.nio;
+
+class FixedArrayByteBuffer extends DirectByteBuffer {
+  private final byte[] array;
+  private final int arrayOffset;
+
+  private FixedArrayByteBuffer(long address,
+                                byte[] array,
+                                int offset,
+                                int capacity,
+                                boolean readOnly)
+  {
+    super(address, capacity, readOnly);
+
+    this.array = array;
+    this.arrayOffset = offset;
+  }
+
+  public static FixedArrayByteBuffer make(int capacity) {
+    long[] address = new long[1];
+    byte[] array = allocateFixed(capacity, address);
+    return new FixedArrayByteBuffer(address[0], array, 0, capacity, false);
+  }
+
+  private static native byte[] allocateFixed(int capacity, long[] address);
+
+  public ByteBuffer asReadOnlyBuffer() {
+    ByteBuffer b = new FixedArrayByteBuffer
+      (address, array, arrayOffset, capacity, true);
+    b.position(position());
+    b.limit(limit());
+    return b;
+  }
+
+  public ByteBuffer slice() {
+    return new FixedArrayByteBuffer
+      (address + position, array, arrayOffset + position, remaining(), true);
+  }
+
+  public String toString() {
+    return "(FixedArrayByteBuffer with address: " + address
+      + " array: " + array
+      + " arrayOffset: " + arrayOffset
+      + " position: " + position
+      + " limit: " + limit
+      + " capacity: " + capacity + ")";
+  }
+}