Implement Audio constructor

[jdm]

Spec:
https://html.spec.whatwg.org/multipage/media.html#the-audio-element (see NamedConstructor usage in WebIDL)
https://html.spec.whatwg.org/multipage/media.html#dom-audio

Code: components/script/dom/webidls/HTMLAudioElement.webidl, components/script/dom/htmlaudioelement.rs

Tests:

• ./mach test-wpt https://github.com/servo/servo/tree/master/tests/wpt/web-platform-tests/html/semantics/embedded-content/the-audio-element
• ./mach test-wpt tests/wpt/web-platform-tests/html/semantics/embedded-content/media-elements
• ./mach test-wpt tests/wpt/web-platform-tests/html/dom/interfaces.https.html
• (see https://github.com/servo/servo/blob/master/tests/wpt/README.md#updating-test-expectations for dealing with unexpected results)

Now that we support actual audio output, we should implement the missing constructor that is used by many websites to create an HTMLAudioElement.

[highfive]

Hi! If you have any questions regarding this issue, feel free to make a comment here, or ask it in the #servo channel in IRC.

If you intend to work on this issue, then add @highfive: assign me to your comment, and I'll assign this to you. 😄

[HrushikeshBodas]

@highfive : assign me
@jdm how can I get started? I have forked and cloned the repo

[highfive]

Hey @HrushikeshBodas! Thanks for your interest in working on this issue. It's now assigned to you!

[jdm]

@HrushikeshBodas There's a similar named constructor for HTMLImageElement, so you can use that as a guide -

servo/components/script/dom/webidls/HTMLImageElement.webidl

Line 6 in 819212e

[HTMLConstructor, NamedConstructor=Image(optional unsigned long width, optional unsigned long height)]

is the webidl, and

servo/components/script/dom/htmlimageelement.rs

Lines 1234 to 1248 in 819212e

	pub fn Image(
	window: &Window,
	width: Option<u32>,
	height: Option<u32>,
	) -> Fallible<DomRoot<HTMLImageElement>> {
	let document = window.Document();
	let image = HTMLImageElement::new(local_name!("img"), None, &document);
	if let Some(w) = width {
	image.SetWidth(w);
	}
	if let Some(h) = height {
	image.SetHeight(h);
	}
	Ok(image)

is the implementation that matches it. https://html.spec.whatwg.org/multipage/embedded-content.html#dom-image is the specification that describes what the implementation is supposed to do.

[jdm]

There was a question on IRC about calling setting the media element's src from this new constructor. You will need to import the HTMLMediaElementMethods trait in order to call the SetSrc method like so: audio_element.upcast::<HTMLMediaElement>().SetSrc(...).