Sync core/timing/ interfaces with their specs, or lack thereof

Source/core/timing/WorkerGlobalScopePerformance.idl

Index: Source/core/timing/WorkerGlobalScopePerformance.idl
diff --git a/Source/core/timing/WorkerGlobalScopePerformance.idl b/Source/core/timing/WorkerGlobalScopePerformance.idl
index 559003a02778b95ddb0bdef56568cc606ba84e76..1682a6e2a65ac98b767ca1bbafae622bd893d2fc 100644
--- a/Source/core/timing/WorkerGlobalScopePerformance.idl
+++ b/Source/core/timing/WorkerGlobalScopePerformance.idl
@@ -28,6 +28,9 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+// TODO(philipj): There is no spec for WorkerGlobalScope.performance:
+// https://github.com/w3c/hr-time/issues/10
+
 partial interface WorkerGlobalScope {
     readonly attribute WorkerPerformance performance;
 };