Bug 1438814 - Use pre-increment operator for height changes. r=birtles

With post increment operator, the first callback doesn't change height at all.

Differential Revision: https://phabricator.services.mozilla.com/D4182

testing/web-platform/tests/css/css-values/reference/vh_not_refreshing_on_chrome-ref.html

@@ -36,10 +36,10 @@
 			var frameTest = document.getElementById('frameTest');
 
 			// let's resize the iframe vertically only, showing that the vh sizes is not updated.
-			if (height <= 300) {
+			if (height < 300) {
 
 				//frameTest.style.width = height++ + "px";
-				frameTest.style.height = height++ + "px";
+				frameTest.style.height = ++height + "px";
 
 				setTimeout(resizeReference, 10);
 

testing/web-platform/tests/css/css-values/vh_not_refreshing_on_chrome.html

@@ -39,10 +39,10 @@
 			var frameTest = document.getElementById('frameTest');
 
 			// let's resize the iframe vertically only, showing that the vh sizes is not updated.
-			if (height <= 300) {
+			if (height < 300) {
 
 				//frameTest.style.width = height++ + "px";
-				frameTest.style.height = height++ + "px";
+				frameTest.style.height = ++height + "px";
 
 				setTimeout(resizeReference, 10);