Make font loading work in workers

src/ol/css.js

@@ -7,6 +7,7 @@
  * @property {Array<string>} families
  * @property {string} style
  * @property {string} weight
+ * @property {string} lineHeight
  */
 
 
@@ -68,8 +69,9 @@ export const CLASS_COLLAPSED = 'ol-collapsed';
 /**
  * Get the list of font families from a font spec.  Note that this doesn't work
  * for font families that have commas in them.
- * @param {string} The CSS font property.
- * @return {FontParameters} The font families (or null if the input spec is invalid).
+ * @param {string} fontSpec The CSS font property.
+ * @param {function(FontParameters):void} callback Called with the font families
+ * (or null if the input spec is invalid).
  */
 export const getFontParameters = (function() {
   /**
@@ -80,26 +82,25 @@ export const getFontParameters = (function() {
    * @type {Object<string, FontParameters>}
    */
   const cache = {};
-  return function(font) {
+  return function(fontSpec, callback) {
     if (!style) {
       style = document.createElement('div').style;
     }
-    if (!(font in cache)) {
-      style.font = font;
+    if (!(fontSpec in cache)) {
+      style.font = fontSpec;
       const family = style.fontFamily;
-      const fontWeight = style.fontWeight;
-      const fontStyle = style.fontStyle;
-      style.font = '';
       if (!family) {
-        return null;
+        callback(null);
       }
       const families = family.split(/,\s?/);
-      cache[font] = {
+      cache[fontSpec] = {
         families: families,
-        weight: fontWeight,
-        style: fontStyle
+        weight: style.fontWeight,
+        style: style.fontStyle,
+        lineHeight: style.lineHeight
       };
+      style.font = '';
     }
-    return cache[font];
+    callback(cache[fontSpec]);
   };
 })();