Using Extend pattern in Clock. Added more robust check for performance.now(). See #2975.

src/core/Clock.js

@@ -14,33 +14,33 @@ THREE.Clock = function ( autoStart ) {
 
 };
 
-THREE.Clock.prototype.start = function () {
+THREE.extend( THREE.Clock.prototype, {
 
-	this.startTime = performance.now !== undefined ? performance.now() : Date.now();
-	this.oldTime = this.startTime;
+	start: function () {
 
-	this.running = true;
+		this.startTime = window.performance !== undefined && window.performance.now !== undefined
+					? window.performance.now()
+					: Date.now();
 
-};
+		this.oldTime = this.startTime;
+		this.running = true;
+	},
 
-THREE.Clock.prototype.stop = function () {
+	stop: function () {
 
 		this.getElapsedTime();
-
 		this.running = false;
 
-};
+	},
 
-THREE.Clock.prototype.getElapsedTime = function () {
+	getElapsedTime: function () {
 
 		this.getDelta();
-
 		return this.elapsedTime;
 
-};
-
+	},
 
-THREE.Clock.prototype.getDelta = function () {
+	getDelta: function () {
 
 		var diff = 0;
 
@@ -52,7 +52,10 @@ THREE.Clock.prototype.getDelta = function () {
 
 		if ( this.running ) {
 
-		var newTime = performance.now !== undefined ? performance.now() : Date.now();
+			var newTime = window.performance !== undefined && window.performance.now !== undefined
+					? window.performance.now()
+					: Date.now();
+
 			diff = 0.001 * ( newTime - this.oldTime );
 			this.oldTime = newTime;
 
@@ -62,4 +65,6 @@ THREE.Clock.prototype.getDelta = function () {
 
 		return diff;
 
-};
+	}
+
+} );