Incorrect IDLs on Web Speech API

Hi again,

E12 added IDL for SpeechSynthesisErrorEvent but it has two errors:


  1.  It uses invalid nested enum syntax.
  2.  It uses invalid Java-style ‘extends’ keyword

It should be:

```webidl
enum SpeechSynthesisErrorCode {
    "canceled",
    "interrupted",
    "audio-busy",
    "audio-hardware",
    "network",
    "synthesis-unavailable",
    "synthesis-failed",
    "language-unavailable",
    "voice-unavailable",
    "text-too-long",
    "invalid-argument",
};

interface SpeechSynthesisErrorEvent : SpeechSynthesisEvent {
    readonly attribute SpeechSynthesisErrorCode error;
};
```

Sincerely,
Kagami Sascha Rosylight