Improve IDB module's SecurityError messages.

LayoutTests/webmidi/requestmidiaccess.html

Index: LayoutTests/webmidi/requestmidiaccess.html
diff --git a/LayoutTests/webmidi/requestmidiaccess.html b/LayoutTests/webmidi/requestmidiaccess.html
index 0696dc7a2544769704da52862ac1dbfd7ad0d56e..9d81ebda5b21d34e9c460848935bb70609692498 100644
--- a/LayoutTests/webmidi/requestmidiaccess.html
+++ b/LayoutTests/webmidi/requestmidiaccess.html
@@ -11,7 +11,7 @@
 description("Tests navigator.requestMIDIAccess.");
 
 var access;
-
+var output;
 function successCallback1(a) {
     access = a;
 
@@ -24,7 +24,7 @@ function successCallback1(a) {
     var inputs = access.inputs();
     var outputs = access.outputs();
     var input = inputs[0];
-    var output = outputs[0];
+    output = outputs[0];
 
     // Validate the values of the attributes on the input and output.
     if (input.id == "MockInputID" &&
@@ -55,6 +55,9 @@ function successCallback1(a) {
     // Test sending of MIDI data with a regular Array giving an explicit timestamp.
     output.send([0x90, 0x45, 0x7f], performance.now());
 
+    // Test sending system exclusive messages. These should throw, since we don't have sysex access.
+    shouldThrow('output.send([0xf1, 0x45, 0x7f])', '"SecurityError: Failed to execute \'send\' on \'MIDIOutput\': permission to send system exclusive messages is denied."');
+
     // Now test System Exclusive access - our test mock should not allow this type of access.
     try {
         navigator.requestMIDIAccess( { sysex: true } ).then(successCallback2, errorCallback2);