Fix Grid scrolling on Firefox (#16865. #17352)

Change-Id: I58ac7c03be2a4d950ecfba609fddf862f2fd966f

client/src/com/vaadin/client/widgets/Escalator.java

             return $entry(function(e) {
                 var deltaX = e.deltaX ? e.deltaX : -0.5*e.wheelDeltaX;
                 var deltaY = e.deltaY ? e.deltaY : -0.5*e.wheelDeltaY;
-                
+
+                // Delta mode 0 is in pixels; we don't need to do anything...
+
+                // A delta mode of 1 means we're scrolling by lines instead of pixels
+                // We need to scale the number of lines by the default line height
+                if(e.deltaMode === 1) {
+                    var brc = esc.@com.vaadin.client.widgets.Escalator::body;
+                    deltaY *= brc.@com.vaadin.client.widgets.Escalator.AbstractRowContainer::getDefaultRowHeight()();
+                }
+
+                // Other delta modes aren't supported
+                if((e.deltaMode !== undefined) && (e.deltaMode >= 2 || e.deltaMode < 0)) {
+                    var msg = "Unsupported wheel delta mode \"" + e.deltaMode + "\"";
+
+                    // Print warning message
+                    esc.@com.vaadin.client.widgets.Escalator::logWarning(*)(msg);
+                }
+
                 // IE8 has only delta y
                 if (isNaN(deltaY)) {
                     deltaY = -0.5*e.wheelDelta;
     private String getSubPartNameSpacer(Element subElement) {
         return body.spacerContainer.getSubPartName(subElement);
     }
+
+    private void logWarning(String message) {
+        getLogger().warning(message);
+    }
 }