border: Get rid of BorderCornerClipSource.

[emilio]

Instead, just add functions to add the instances directly, avoiding the
intermediate allocation and deindenting a bunch of the code.

This should have no behavior change.

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This change is 

[emilio]

r? @kvark or anyone else?

I'm sorry, github is terrible at flagging indentation changes. :(

[kvark]

a few notes, no blockers

Reviewed 1 of 1 files at r1.
Reviewable status: all files reviewed, 4 unresolved discussions (waiting on @emilio)

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webrender/src/border.rs, line 244 at r1 (raw file):

}

fn outer_and_clip_sign(

let's have it starting with a verb, since it's not an accessor method

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webrender/src/border.rs, line 253 at r1 (raw file):

        BorderSegment::BottomRight => DeviceVector2D::new(1.0, 1.0),
        BorderSegment::BottomLeft => DeviceVector2D::new(0.0, 1.0),
        _ => unreachable!(),

panic would probably be more appropriate

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webrender/src/border.rs, line 260 at r1 (raw file):

    );

    let clip_sign = DeviceVector2D::new(

nit: could use vector operations?

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webrender/src/border.rs, line 282 at r1 (raw file):

        compute_half_dash(average_border_width, ellipse.total_arc_length);

    if num_half_dashes == 0 {

uuh, anticipating rebase issues in #3049

[emilio]

nit: could use vector operations?

I couldn't do this: no implementation for {float} - euclid::TypedVector2D<f32, webrender_api::DevicePixel>

[emilio]

@bors-servo r=kvark

[bors-servo]

📌 Commit 88353b7 has been approved by kvark

[emilio]

(Rest of comments should be addressed)

[bors-servo]

⌛ Testing commit 88353b7 with merge 0f14252...

[bors-servo]

☀️ Test successful - status-appveyor, status-taskcluster
Approved by: kvark
Pushing 0f14252 to master...