Drop [LegacyInterfaceTypeChecking] where trivial in Web Audio

third_party/WebKit/LayoutTests/webaudio/resources/audio-testing.js

Index: third_party/WebKit/LayoutTests/webaudio/resources/audio-testing.js
diff --git a/third_party/WebKit/LayoutTests/webaudio/resources/audio-testing.js b/third_party/WebKit/LayoutTests/webaudio/resources/audio-testing.js
index a838881c5a688d4502fc8b06e90e07e4cc498399..875891b1ff59f1a5a4c94737ba32bd02da581cff 100644
--- a/third_party/WebKit/LayoutTests/webaudio/resources/audio-testing.js
+++ b/third_party/WebKit/LayoutTests/webaudio/resources/audio-testing.js
@@ -597,6 +597,8 @@ var Should = (function () {
                 this._testPassed('threw an exception of type ' + error.name);
             else if (error.name === errorType)
                 this._testPassed('threw ' + errorType + ': ' + error.message);
+            else if (errorType in self && error instanceof self[errorType])
+                this._testPassed('threw ' + errorType + ': ' + error.message);

[Raymond Toy, 2015/11/30 19:00:17]

My Javascript-fu is too weak to understand what this is doing.  Can you explain
it to me?

[philipj_slow, 2015/11/30 19:21:59]

This is to handle the "native" error types that have individual interfaces,
listed in http://heycam.github.io/webidl/#idl-exceptions

When the errorType is "TypeError", it will see that window.TypeError is defined
and test `error instanceof TypeError`. I used self instead of window just in
case this framework is also used in workers, or will be.

[hongchan, 2015/11/30 19:40:40]

Okay, the worker part convinced me. However, isn't this a bit more readable?

self.hasOwnProperty(errorType)

(...sorry, I am not a reviewer but wanted to contribute here.)

[philipj_slow, 2015/11/30 20:48:30]

This assumes that interface objects (TypeError, Document, etc) are own
properties on the global object as opposed to attributes on Window.prototype,
which I was not sure about until I checked it:

http://heycam.github.io/webidl/#es-interfaces

Turns out it's supposed to be on the global object, so I've changed it as you
suggested.

             else
                 this._testFailed('threw ' + error.name + ' instead of ' + exception);
         }