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..2775d21dc05cf7d9823eaa9ceb26705f9af4ead7 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 Performance in workers:

[Kunihiko Sakamoto, 2015/07/10 06:37:55]

Performance is defined here as [Exposed=(Window,Worker)]:
https://w3c.github.io/performance-timeline/#the-performance-interface

[philipj_slow, 2015/07/10 08:18:14]

You're right, this was a bit confused. There's a spec for exposing the interface
in workers, but no way to get an instance in workers. I've updated this and
related TODOs to be less wrong :)

[Kunihiko Sakamoto, 2015/07/10 08:28:56]

Got it. :) Thanks!

+// https://github.com/w3c/hr-time/issues/10
+
 partial interface WorkerGlobalScope {
     readonly attribute WorkerPerformance performance;
 };