Merge "Add MediaWiki-Timestamp header to ResourceLoader requests"

diff --combined includes/resourceloader/ResourceLoader.php
index e6cb5eb,54cc6e5..508be2f
--- 1/includes/resourceloader/ResourceLoader.php
--- 2/includes/resourceloader/ResourceLoader.php
+++ b/includes/resourceloader/ResourceLoader.php
@@@ -224,8 -224,7 +224,8 @@@ class ResourceLoader implements LoggerA
                                if ( $options['cacheReport'] ) {
                                        $result .= "\n/* cache key: $key */";
                                }
 -                              $cache->set( $key, $result );
 +                              // Set a TTL since HHVM's APC doesn't have any limitation or eviction logic.
 +                              $cache->set( $key, $result, 24 * 3600 );
                        } catch ( Exception $e ) {
                                MWExceptionHandler::logException( $e );
                                $this->logger->warning( 'Minification failed: {exception}', array(
@@@ -814,6 -813,11 +814,11 @@@
                        $exp = min( $maxage, $smaxage );
                        header( 'Expires: ' . wfTimestamp( TS_RFC2822, $exp + time() ) );
                }
+ 
+               // Send the current time expressed as fractional seconds since epoch,
+               // with microsecond precision. This helps distinguish hits from misses
+               // in edge caches.
+               header( 'MediaWiki-Timestamp: ' . microtime( true ) );
        }
  
        /**