Improve performance of Util.collectionEquals (#16968).

This change checks the length of both collections first before iterating
them. This massively speeds up the comparison in case the collections do
not have the same length.

Also in the case where the lengths are equal, this saves the
collection2.hasNext() checks.

Change-Id: If1325f3581d12bf742d77fbf8b0f89511fa11252

client/src/com/vaadin/client/Util.java

@@ -825,30 +825,29 @@ public class Util {
      * @return true if the collections contain the same elements in the same
      *         order, false otherwise
      */
-    public static boolean collectionsEquals(Collection collection1,
-            Collection collection2) {
+    public static boolean collectionsEquals(Collection<?> collection1,
+            Collection<?> collection2) {
         if (collection1 == null) {
             return collection2 == null;
         }
         if (collection2 == null) {
             return false;
         }
-        Iterator<Object> collection1Iterator = collection1.iterator();
-        Iterator<Object> collection2Iterator = collection2.iterator();
+
+        if (collection1.size() != collection2.size()) {
+            return false;
+        }
+
+        Iterator<?> collection1Iterator = collection1.iterator();
+        Iterator<?> collection2Iterator = collection2.iterator();
 
         while (collection1Iterator.hasNext()) {
-            if (!collection2Iterator.hasNext()) {
-                return false;
-            }
             Object collection1Object = collection1Iterator.next();
             Object collection2Object = collection2Iterator.next();
             if (collection1Object != collection2Object) {
                 return false;
             }
         }
-        if (collection2Iterator.hasNext()) {
-            return false;
-        }
 
         return true;
     }