Conditionally allow Gerrit to load in IFrame

Introduce new configuration option (gerrit.canLoadInIFrame) to allow
loading Gerrit in IFrame. By default it is set to 'false' to keep
current behavior.

Change-Id: Ie13b6141a9dfb8a18348fc778fb5f6083f95bd14
Signed-off-by: Dariusz Luksza <dariusz@luksza.org>

gerrit-gwtui/src/main/java/com/google/gerrit/client/Gerrit.java

@@ -405,7 +405,9 @@ public class Gerrit implements EntryPoint {
 
   @Override
   public void onModuleLoad() {
-    UserAgent.assertNotInIFrame();
+    if (!canLoadInIFrame()) {
+      UserAgent.assertNotInIFrame();
+    }
     setXsrfToken();
 
     KeyUtil.setEncoderImpl(new KeyUtil.Encoder() {
@@ -507,6 +509,10 @@ public class Gerrit implements EntryPoint {
     }));
   }
 
+  private native boolean canLoadInIFrame() /*-{
+    return $wnd.gerrit_hostpagedata.canLoadInIFrame || false;
+  }-*/;
+
   private static void initHostname() {
     myHost = Location.getHostName();
     final int d1 = myHost.indexOf('.');