[css-typed-om] Minor issue in arithmetic methods add(), min(), and max() of CSSNumericValue

[johannesodland]

Several of the arithmetic methods are referring to this's unit internal slot.
However, this might be an instance of some other class than CSSUnitValue.
As a result it won't have a unit internal slot.

Example from step 2 of add(...values):

return a new CSSUnitValue whose unit internal slot is set to this’s unit internal slot

This affects the following methods:

• add(...values) method: this might be a CSSMathSum object
• min(...values): this might be a CSSMathMin object
• max(...values): this might be a CSSMathMax object

The issue can be fixed by defining unit in the steps:

If all of the items in values are CSSUnitValues and have the same unit unit, return a new CSSUnitValue whose unit internal slot is set to unit

[tabatkins]

Oh whoops, you're right, I meant to check that all the passed args and this are CSSUnitValues.

(Your suggested fix won't work, since we need to include this's value and make sure it's compatible.)

[tabatkins]

Wait, no, step 2 takes care of that already, by prepending this to values. Since step 3 checks that all the items in values are CSSUnitValues with the same type, that means that this must be as well, so the algo is sound. Same applies to all the other methods - their step 2 checks if this is a compatible type that can be directly altered, otherwise it shoves this into the list and works on that.

[tabatkins]

Sigh, nm, I see the bug.