add new analysis server preferences to experimental page

editor/tools/plugins/com.google.dart.tools.ui/src/com/google/dart/tools/ui/internal/preferences/ValidIntListener.java

Index: editor/tools/plugins/com.google.dart.tools.ui/src/com/google/dart/tools/ui/internal/preferences/ValidIntListener.java
diff --git a/editor/tools/plugins/com.google.dart.tools.ui/src/com/google/dart/tools/ui/internal/preferences/ValidIntListener.java b/editor/tools/plugins/com.google.dart.tools.ui/src/com/google/dart/tools/ui/internal/preferences/ValidIntListener.java
new file mode 100644
index 0000000000000000000000000000000000000000..913a2ce1289b398fbbacdcafc7b6a520e32fdef5
--- /dev/null
+++ b/editor/tools/plugins/com.google.dart.tools.ui/src/com/google/dart/tools/ui/internal/preferences/ValidIntListener.java
@@ -0,0 +1,30 @@
+package com.google.dart.tools.ui.internal.preferences;
+
+import org.eclipse.swt.widgets.Event;
+import org.eclipse.swt.widgets.Listener;
+
+/**
+ * Listener that only allows digits to be entered into a text field
+ */
+class ValidIntListener implements Listener {
+  @Override
+  public void handleEvent(Event e) {
+    String txt = e.text;
+    // Allow for delete
+    if (txt.isEmpty()) {
+      return;
+    }
+    try {
+      // Only allow digits
+      int num = Integer.parseInt(txt);
+      if (num >= 0) {
+        return;
+      }
+    } catch (NumberFormatException nfe) {
+      // Error
+    }
+
+    e.doit = false;
+    return;
+  }
+}