Fix swipe-back in iOS

trace/trace.d.ts

@@ -41,6 +41,12 @@ declare module "trace" {
      */
     export function addCategories(categories: string);
 
+    /**
+     * Check if category is already set in trace module.
+     * @param category The category to check.
+     */
+    export function isCategorySet(category: string): boolean;
+
     /**
      * Writes a message using the available writers.
      * @param message The message to be written.

trace/trace.ts

@@ -14,6 +14,10 @@ export function disable() {
     _enabled = false;
 }
 
+export function isCategorySet(category: string): boolean {
+    return category in _categories;
+}
+
 export function addWriter(writer: definition.TraceWriter) {
     _writers.push(writer);
 }