Clone windowcapability before returning to user

Author: crokita

lib/js/src/manager/SystemCapabilityManager.js

@@ -194,8 +194,11 @@ class SystemCapabilityManager extends _SubManagerBase {
                 currentWindowId = PredefinedWindows.DEFAULT_WINDOW;
             }
             if (currentWindowId === windowId) {
-                windowCapability.setWindowID(windowId);
-                return windowCapability;
+                // Clone WindowCapability to prevent modification of stored WindowCapability in SystemCapabilityManager
+                const windowCapabilityCopy = new WindowCapability(JSON.parse(JSON.stringify(windowCapability.getParameters())));
+                // A null windowID is assumed to be the DefaultWindow according to the spec, but that can be hard for developers to check, so set it explicitly.
+                windowCapabilityCopy.setWindowID(windowId);
+                return windowCapabilityCopy;
             }
         }
         return null;