return empty responses to avoid connections errors in Chrome

lib/frame-tree/content/content-frame-tree.js

@@ -48,6 +48,7 @@ this.singlefile.lib.frameTree.content.frames = this.singlefile.lib.frameTree.con
 			browser.runtime.onMessage.addListener(message => {
 				if (message.method == INIT_RESPONSE_MESSAGE) {
 					initResponse(message);
+					return Promise.resolve({});
 				}
 			});
 		}

lib/lazy/content/content-lazy-loader.js

@@ -136,6 +136,7 @@ this.singlefile.lib.lazy.content.loader = this.singlefile.lib.lazy.content.loade
 				if (message.method == "content.onLazyTimeout" && message.id == timeoutId) {
 					browser.runtime.onMessage.removeListener(timeoutCallback);
 					callback();
+					return Promise.resolve({});
 				}
 			};
 			browser.runtime.onMessage.addListener(timeoutCallback);