Initialize XCallback.extra only if needed

This is a little API change, but it doesn't seemed to be used often
anyway. However, it improves the speed of hooks and allocates less
unneeded objects that need to be GC'd later.

src/de/robv/android/xposed/callbacks/XCallback.java

@@ -18,13 +18,7 @@ public XCallback(int priority) {
 
 	public static class Param {
 		public final TreeSet<? extends XCallback> callbacks;
-		/**
-		 * This can be used to store anything for the scope of the callback.
-		 * Use this instead of instance variables.
-		 * @see #getObjectExtra
-		 * @see #setObjectExtra
-		 */
-		public final Bundle extra = new Bundle();
+		private Bundle extra;
 
 		protected Param() {
 			callbacks = null;
@@ -37,17 +31,29 @@ protected Param(TreeSet<? extends XCallback> callbacks) {
 			}
 		}
 
+		/**
+		 * This can be used to store anything for the scope of the callback.
+		 * Use this instead of instance variables.
+		 * @see #getObjectExtra
+		 * @see #setObjectExtra
+		 */
+		public synchronized Bundle getExtra() {
+			if (extra == null)
+				extra = new Bundle();
+			return extra;
+		}
+
 		/** @see #setObjectExtra */
 		public Object getObjectExtra(String key) {
-			Serializable o = extra.getSerializable(key);
+			Serializable o = getExtra().getSerializable(key);
 			if (o instanceof SerializeWrapper)
 				return ((SerializeWrapper) o).object;
 			return null;
 		}
 
 		/** Provides a wrapper to store <code>Object</code>s in <code>extra</code>. */
 		public void setObjectExtra(String key, Object o) {
-			extra.putSerializable(key, new SerializeWrapper(o));
+			getExtra().putSerializable(key, new SerializeWrapper(o));
 		}
 
 		private static class SerializeWrapper implements Serializable {