Example player playback position and buffered UI

[cpearce]

• Add Mirror and Canonical to share values between threads.
• Use Mirror/Canonical instead of channels to share duration, time, buffered, and video dimensions between threads in example player. This makes more sense than using channels where we must do a try_recv() in a loop to get the latest value.
• Add UI to render the current playback position, and the buffered ranges.
• We're currently not updating the buffered ranges when data comes in over the network, so it's not very impressive yet. I'll fix that in a later PR. We'll probably need to rework the NetworkResource trait to make that possible.

[cpearce]

@nox r?

[nox]

r=me with the trait removed or renamed.

[bors-servo]

:umbrella: The latest upstream changes (presumably #114) made this pull request unmergeable. Please resolve the merge conflicts.

[cpearce]

@nox using an inherent function isn't working:

error[E0116]: cannot define inherent impl for a type outside of the crate where the type is defined --> src/bin/test-player.rs:276:1	276	/ impl LayoutPrimitiveInfo { 277		pub fn to(&self, x2: i32, y2: i32) -> LayoutRect { 278		LayoutRect::new( 279		LayoutPoint::new(self.0 as f32, self.1 as f32), ...	282		} 283		}		_^ impl for type defined outside of crate.

= note: define and implement a trait or new type instead

error: aborting due to previous error

Is there some other way this can be made to work?

[nox]

I had assumed that LayoutPrimitiveInfo was our own type, sorry. Let's just merge it as is, r=me once it's rebased.

[cpearce]

@bors-servo r=nox

[bors-servo]

:pushpin: Commit 1543745 has been approved by nox

[bors-servo]

:hourglass: Testing commit 1543745458274db0f3f023044b14cb5aaf9805c2 with merge ecb0cc7bfdf9629e550f6d13962c7f8f780a0d0c...

[bors-servo]

:sunny: Test successful - status-travis Approved by: nox Pushing ecb0cc7bfdf9629e550f6d13962c7f8f780a0d0c to master...