Add extra color methods:

? saturateColor(color, amount)
? desaturateColor(color, amount)
? greyscale(color)
? lighten(color, amount)
? darken(color, amount)
? spin(color, hue_angle)

Contributed by Yves Brissaud (@eunomie on GitHub)

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=107215377

README.md

@@ -135,6 +135,12 @@ for details, but here are the functions and the arguments that they take:
   * `addHsbToCssColor(baseColor, hueToAdd, saturationToAdd, brightnessToAdd)`
   * `makeContrastingColor(color, similarityIndex)`
   * `adjustBrightness(color, brightness)`
+  * `saturateColor(color, saturationToAdd)` increase saturation in HSL color space
+  * `desaturateColor(color, saturationToRemove)` decrease saturation in HSL color space
+  * `greyscale(color)` full desaturation of a color in HSL color space
+  * `lighten(color, lightnessToAdd)` increase the lightness in HSL color space
+  * `darken(color, lightnessToRemove)` decrease the lightness in HSL color space
+  * `spin(color, hueAngle)` increase or decrease hue of the color, like rotating in a color wheel
 
 There is also a `selectFrom()` function that behaves like the ternary operator:
 
@@ -554,6 +560,7 @@ to create **`dialog.soy.js`**:
 ```
 java -jar SoyToJsSrcCompiler.jar \\
     --shouldProvideRequireSoyNamespaces \\
+    --codeStyle concat \\
     --cssHandlingScheme GOOG \\
     --outputPathFormat '{INPUT_FILE_NAME_NO_EXT}.soy.js' \\
     dialog.soy

src/com/google/common/css/compiler/gssfunctions/ColorUtil.java

@@ -17,6 +17,7 @@
 package com.google.common.css.compiler.gssfunctions;
 
 import java.awt.Color;
+import java.lang.Math;
 
 /**
  * Utility functions to deal with colors.
@@ -25,9 +26,14 @@
  */
 class ColorUtil {
 
+  /** Index of Hue in HSB and HSL array. */
   static final int H = 0;
+  /** Index of Saturation in HSB and HSL array. */
   static final int S = 1;
+  /** Index of Brightness in HSB array. */
   static final int B = 2;
+  /** Index of Lightness in HSL array. */
+  static final int L = 2;
 
   static float[] toHsb(Color color) {
     return Color.RGBtoHSB(
@@ -43,6 +49,72 @@ static Color hsbToColor(float[] inputHsb) {
     return Color.getHSBColor(inputHsb[H], inputHsb[S], inputHsb[B]);
   }
 
+  /**
+   * Convert a color in HSB color space to one in HSL color space.
+   *
+   * @param inputHsb HSB color in a array of three floats, 0 is Hue, 1 is
+   *     Saturation and 2 is Brightness
+   * @return HSL color in array of three floats, 0 is Hue, 1 is
+   *     Saturation and 2 is Lightness
+   */
+  static float[] hsbToHsl(float[] inputHsb) {
+    float hHsb = inputHsb[H];
+    float sHsb = inputHsb[S];
+    float bHsb = inputHsb[B];
+
+    float hHsl = hHsb;
+    float lHsl = bHsb * (2 - sHsb) / 2;
+    float sHsl = bHsb * sHsb / (1 - Math.abs(2 * lHsl - 1));
+
+    float[] hsl = {hHsl, sHsl, lHsl};
+
+    return hsl;
+  }
+
+  /**
+   * Get the HSL values of a color.
+   *
+   * @param color Color to get the HSL values
+   * @return array of floats representing the color in HSL color space
+   */
+  static float[] toHsl(Color color) {
+    return hsbToHsl(toHsb(color));
+  }
+
+  /**
+   * Convert a color in HSL color space to one in HSB color space.
+   *
+   * @param inputHsl HSL color in a array of three floats, 0 is Hue, 1 is
+   *     Saturation and 2 is Lightness
+   * @return HSB color in array of three floats, 0 is Hue, 1 is
+   *     Saturation and 2 is Brightness
+   */
+  static float[] hslToHsb(float[] inputHsl) {
+    float hHsl = inputHsl[H];
+    float sHsl = inputHsl[S];
+    float lHsl = inputHsl[L];
+
+    float hHsb = hHsl;
+    float bHsb = (2 * lHsl + sHsl * (1 - Math.abs(2 * lHsl - 1))) / 2;
+    float sHsb = 2 * (bHsb - lHsl) / bHsb;
+
+    float[] hsb = {hHsb, sHsb, bHsb};
+
+    return hsb;
+  }
+
+  /**
+   * Get the color from the HSL floats
+   *
+   * @param inputHsl HSL color
+   * @return Java color
+   */
+  static Color hslToColor(float[] inputHsl) {
+    float[] hsb = hslToHsb(inputHsl);
+
+    return Color.getHSBColor(hsb[H], hsb[S], hsb[B]);
+  }
+
   /**
    * Tests whether the given colors are contrasting colors, according to the
    * test described in the W3C accessibility evaluation working draft