Add deprecation warning to requestMediaKeySystemAccess on insecure origins.

Source/core/frame/UseCounter.cpp

Index: Source/core/frame/UseCounter.cpp
diff --git a/Source/core/frame/UseCounter.cpp b/Source/core/frame/UseCounter.cpp
index e088ff7ada4bba9663166034b949b2660d8c5b1b..5af04c876805c118e2e842409bd92a300c14df7b 100644
--- a/Source/core/frame/UseCounter.cpp
+++ b/Source/core/frame/UseCounter.cpp
@@ -903,6 +903,9 @@ String UseCounter::deprecationMessage(Feature feature)
     case FullscreenInsecureOrigin:
         return "requestFullscreen() is deprecated on insecure origins, and support will be removed in the future. You should consider switching your application to a secure origin, such as HTTPS. See https://goo.gl/rStTGz for more details.";
 
+    case EncryptedMediaInsecureOrigin:
+        return "requestMediaKeySystemAccess() is deprecated on insecure origins in the specification. Support will be removed in the future. You should consider switching your application to a secure origin, such as HTTPS. See https://goo.gl/rStTGz for more details.";
+
     case PushSubscriptionId:
         return "'PushSubscription.subscriptionId' is deprecated and is now included in 'PushSubscription.endpoint'. It will be removed in Chrome 45, around August 2015.";