Adding HSLColor and color 'within' matchers for HSVColor and HSLColor (#18294)

This adds an HSLColor class which uses a perceptual color space based upon human perception of colored light (as opposed to HSV, which is based on pigment colors).

You can see the difference in the color spaces here: https://en.wikipedia.org/wiki/HSL_and_HSV

I also added a "within" matcher for both HSLColor and HSVColor that will check if the (floating point) color components are within a certain error.

And tests.

examples/flutter_gallery/lib/demo/material/chip_demo.dart

@@ -167,7 +167,7 @@ class _ChipDemoState extends State<ChipDemo> {
   Color _nameToColor(String name) {
     assert(name.length > 1);
     final int hash = name.hashCode & 0xffff;
-    final double hue = 360.0 * hash / (1 << 15);
+    final double hue = (360.0 * hash / (1 << 15)) % 360.0;
     return new HSVColor.fromAHSV(1.0, hue, 0.4, 0.90).toColor();
   }
 

packages/flutter_test/lib/src/matchers.dart

@@ -653,6 +653,8 @@ typedef num AnyDistanceFunction(Null a, Null b);
 
 const Map<Type, AnyDistanceFunction> _kStandardDistanceFunctions = const <Type, AnyDistanceFunction>{
   Color: _maxComponentColorDistance,
+  HSVColor: _maxComponentHSVColorDistance,
+  HSLColor: _maxComponentHSLColorDistance,
   Offset: _offsetDistance,
   int: _intDistance,
   double: _doubleDistance,
@@ -671,6 +673,22 @@ double _maxComponentColorDistance(Color a, Color b) {
   return delta.toDouble();
 }
 
+// Compares hue by converting it to a 0.0 - 1.0 range, so that the comparison
+// can be a similar error percentage per component.
+double _maxComponentHSVColorDistance(HSVColor a, HSVColor b) {
+  double delta = math.max<double>((a.saturation - b.saturation).abs(), (a.value - b.value).abs());
+  delta = math.max<double>(delta, ((a.hue - b.hue) / 360.0).abs());
+  return math.max<double>(delta, (a.alpha - b.alpha).abs());
+}
+
+// Compares hue by converting it to a 0.0 - 1.0 range, so that the comparison
+// can be a similar error percentage per component.
+double _maxComponentHSLColorDistance(HSLColor a, HSLColor b) {
+  double delta = math.max<double>((a.saturation - b.saturation).abs(), (a.lightness - b.lightness).abs());
+  delta = math.max<double>(delta, ((a.hue - b.hue) / 360.0).abs());
+  return math.max<double>(delta, (a.alpha - b.alpha).abs());
+}
+
 double _rectDistance(Rect a, Rect b) {
   double delta = math.max<double>((a.left - b.left).abs(), (a.top - b.top).abs());
   delta = math.max<double>(delta, (a.right - b.right).abs());