Use Math.cosh of ES6/2015 if available

src/ol/math.js

@@ -17,13 +17,30 @@ ol.math.clamp = function(value, min, max) {
 
 
 /**
+ * Return the hyperbolic cosine of a given number. The method will use the
+ * native `Math.cosh` function if it is available, otherwise the hyperbolic
+ * cosine will be calculated via the reference implementation of the Mozilla
+ * developer network.
+ *
  * @param {number} x X.
  * @return {number} Hyperbolic cosine of x.
  */
-ol.math.cosh = function(x) {
-  var y = Math.exp(x);
-  return (y + 1 / y) / 2;
-};
+ol.math.cosh = (function() {
+  // Wrapped in a iife, to save the overhead of checking for the native
+  // implementation on every invocation.
+  var cosh;
+  if ('cosh' in Math) {
+    // The environment supports the native Math.cosh function, use it…
+    cosh = Math.cosh;
+  } else {
+    // … else, use the reference implementation of MDN:
+    cosh = function(x) {
+      var y = Math.exp(x);
+      return (y + 1 / y) / 2;
+    };
+  }
+  return cosh;
+}());
 
 
 /**