Added support PORTLET_CONTEXT for vaadin.resources.path value (#14640)

Change-Id: Ie801a17ed1eff29a7dc6be61755241777071ab8f

server/src/com/vaadin/server/Constants.java

@@ -162,4 +162,6 @@ public interface Constants {
     static final String PORTAL_PARAMETER_VAADIN_WIDGETSET = "vaadin.widgetset";
     static final String PORTAL_PARAMETER_VAADIN_RESOURCE_PATH = "vaadin.resources.path";
     static final String PORTAL_PARAMETER_VAADIN_THEME = "vaadin.theme";
+
+    static final String PORTLET_CONTEXT = "PORTLET_CONTEXT";
 }

server/src/com/vaadin/server/VaadinPortletService.java

@@ -162,7 +162,11 @@ public class VaadinPortletService extends VaadinService {
         String staticFileLocation = getParameter(request,
                 Constants.PORTAL_PARAMETER_VAADIN_RESOURCE_PATH, "/html");
 
-        return trimTrailingSlashes(staticFileLocation);
+        if (Constants.PORTLET_CONTEXT.equals(staticFileLocation)) {
+            return request.getContextPath();
+        } else{
+            return trimTrailingSlashes(staticFileLocation);
+        }
     }
 
     private PortletContext getPortletContext() {