Allow "Keyboard Shortcuts" help popup to be closed with Escape key

Bug: Issue 1996
Change-Id: I7391acad508657b3c7d3e3211bb7a51778f4a7e9

gerrit-gwtexpui/src/main/java/com/google/gwtexpui/globalkey/client/KeyHelpPopup.java

@@ -16,8 +16,11 @@ package com.google.gwtexpui.globalkey.client;
 
 import com.google.gwt.event.dom.client.ClickEvent;
 import com.google.gwt.event.dom.client.ClickHandler;
+import com.google.gwt.event.dom.client.KeyCodes;
 import com.google.gwt.event.dom.client.KeyPressEvent;
 import com.google.gwt.event.dom.client.KeyPressHandler;
+import com.google.gwt.event.dom.client.KeyUpEvent;
+import com.google.gwt.event.dom.client.KeyUpHandler;
 import com.google.gwt.user.client.DOM;
 import com.google.gwt.user.client.ui.Anchor;
 import com.google.gwt.user.client.ui.FlowPanel;
@@ -38,7 +41,7 @@ import java.util.List;
 
 
 public class KeyHelpPopup extends PluginSafePopupPanel implements
-    KeyPressHandler {
+    KeyPressHandler, KeyUpHandler {
   private final FocusPanel focus;
 
   public KeyHelpPopup() {
@@ -77,6 +80,7 @@ public class KeyHelpPopup extends PluginSafePopupPanel implements
     DOM.setStyleAttribute(focus.getElement(), "outline", "0px");
     DOM.setElementAttribute(focus.getElement(), "hideFocus", "true");
     focus.addKeyPressHandler(this);
+    focus.addKeyUpHandler(this);
     add(focus);
   }
 
@@ -100,6 +104,13 @@ public class KeyHelpPopup extends PluginSafePopupPanel implements
     hide();
   }
 
+  @Override
+  public void onKeyUp(final KeyUpEvent event) {
+    if (event.getNativeKeyCode() == KeyCodes.KEY_ESCAPE) {
+      hide();
+    }
+  }
+
   private void populate(final Grid lists) {
     int end[] = new int[5];
     int column = 0;