Add the cache key to the filter output, like what we do with the parser cache, to make it easier to debug filter issues.

includes/resourceloader/ResourceLoader.php

@@ -152,9 +152,11 @@ class ResourceLoader {
 					$result = JavaScriptDistiller::stripWhiteSpace(
 						$data, $wgResourceLoaderMinifyJSVerticalSpace
 					);
+					$result .= "\n\n/* cache key: $key */\n";
 					break;
 				case 'minify-css':
 					$result = CSSMin::minify( $data );
+					$result .= "\n\n/* cache key: $key */\n";
 					break;
 			}