color: Add a way to hook into the parsing of the components of the color functions.

[emilio]

This way we'll be able to implement calc-in-color without duplicating a ton of
code for calc() handling in Servo.

Minor version bump because the API is not broken, just expanded to support
providing an optional ColorComponentParser.

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This change is 

[emilio]

r? @SimonSapin

[SimonSapin]

Do you have a Servo patch yet that uses this API? (To make sure it is sufficient, e.g. in BasicParseError v.s. ParseError.)

r+ with changes if so

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Reviewed 2 of 2 files at r1.
Review status: all files reviewed at latest revision, 2 unresolved discussions.

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src/color.rs, line 151 at r1 (raw file):

pub enum NumberOrPercentage {
    Number(f32),
    Percentage(f32),

Please use Percentage { unit_value: f32 } to remind that "100%" is represented as 1.0_f32, not 100.0_f32, and add a doc-comment explaining that. (And maybe Number { value : f32 } for consistency.)

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src/color.rs, line 155 at r1 (raw file):

impl NumberOrPercentage {
    fn get(&self) -> f32 {

Please rename this to unit_value(), with a doc comment repeating the 100% => 1.0 thing.

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Comments from Reviewable

[emilio]

Can you take another look? Had to add a couple things for servo.

[SimonSapin]

@bors-servo r+

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Reviewed 2 of 2 files at r2.
Review status: all files reviewed at latest revision, all discussions resolved.

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Comments from Reviewable

[bors-servo]

📌 Commit 97890a3 has been approved by SimonSapin

[bors-servo]

⌛ Testing commit 97890a3 with merge 6e8a5a4...

[bors-servo]

☀️ Test successful - status-travis
Approved by: SimonSapin
Pushing 6e8a5a4 to master...