SideBySide2: Restore focus to CM B after showing key binding help

This way ?, ? then / works as expected, the user can open the
help close it again and immediately use a binding in the right
side CM3 instance.

Change-Id: Ia3eede648ca2c79bda028f32e78c4295a61d3e33

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

@@ -14,18 +14,27 @@
 
 package com.google.gwtexpui.globalkey.client;
 
+import com.google.gwt.event.dom.client.FocusEvent;
+import com.google.gwt.event.dom.client.FocusHandler;
 import com.google.gwt.event.dom.client.KeyPressEvent;
 import com.google.gwt.event.logical.shared.CloseEvent;
 import com.google.gwt.event.logical.shared.CloseHandler;
+import com.google.gwt.event.shared.EventBus;
+import com.google.gwt.event.shared.HandlerRegistration;
+import com.google.gwt.event.shared.SimpleEventBus;
 import com.google.gwt.user.client.Window;
 import com.google.gwt.user.client.ui.PopupPanel;
 import com.google.gwt.user.client.ui.PopupPanel.PositionCallback;
 
-
 public class ShowHelpCommand extends KeyCommand {
   public static final ShowHelpCommand INSTANCE = new ShowHelpCommand();
+  private static final EventBus BUS = new SimpleEventBus();
   private static KeyHelpPopup current;
 
+  public static HandlerRegistration addFocusHandler(FocusHandler fh) {
+    return BUS.addHandler(FocusEvent.getType(), fh);
+  }
+
   public ShowHelpCommand() {
     super(0, '?', KeyConstants.I.showHelp());
   }
@@ -36,7 +45,6 @@ public class ShowHelpCommand extends KeyCommand {
       // Already open? Close the dialog.
       //
       current.hide();
-      current = null;
       return;
     }
 
@@ -45,6 +53,7 @@ public class ShowHelpCommand extends KeyCommand {
       @Override
       public void onClose(final CloseEvent<PopupPanel> event) {
         current = null;
+        BUS.fireEvent(new FocusEvent() {});
       }
     });
     current = help;

gerrit-gwtui/src/main/java/com/google/gerrit/client/diff/SideBySide2.java

@@ -44,6 +44,8 @@ import com.google.gwt.core.client.Scheduler.ScheduledCommand;
 import com.google.gwt.dom.client.Element;
 import com.google.gwt.dom.client.NativeEvent;
 import com.google.gwt.dom.client.Style.Unit;
+import com.google.gwt.event.dom.client.FocusEvent;
+import com.google.gwt.event.dom.client.FocusHandler;
 import com.google.gwt.event.dom.client.KeyCodes;
 import com.google.gwt.event.dom.client.KeyPressEvent;
 import com.google.gwt.event.logical.shared.ResizeEvent;
@@ -458,12 +460,19 @@ public class SideBySide2 extends Screen {
     } else {
       keysComment = null;
     }
+
     removeKeyHandlerRegistrations();
     handlers.add(GlobalKey.add(this, keysNavigation));
     if (keysComment != null) {
       handlers.add(GlobalKey.add(this, keysComment));
     }
     handlers.add(GlobalKey.add(this, keysAction));
+    handlers.add(ShowHelpCommand.addFocusHandler(new FocusHandler() {
+      @Override
+      public void onFocus(FocusEvent event) {
+        cmB.focus();
+      }
+    }));
   }
 
   private void display(final CommentsCollections comments) {