Flipping the direction of WheelEvent.deltaX/Y to follow standards

sdk/lib/html/dart2js/html_dart2js.dart

Index: sdk/lib/html/dart2js/html_dart2js.dart
diff --git a/sdk/lib/html/dart2js/html_dart2js.dart b/sdk/lib/html/dart2js/html_dart2js.dart
index 95c8ab0732542b22c791417b26ccd2f72b485a1d..a541a048873201b4cb6a90b8cd7988f82df1e38b 100644
--- a/sdk/lib/html/dart2js/html_dart2js.dart
+++ b/sdk/lib/html/dart2js/html_dart2js.dart
@@ -26438,6 +26438,11 @@ class WheelEvent extends MouseEvent native "*WheelEvent" {
       eventType = 'MouseScrollEvents';
     }
     final event = document.$dom_createEvent(eventType);
+    // If polyfilling, then flip these to match W3C wheel spec.
+    if (JS('bool', '#.deltaY === undefined', event)) {
+      deltaX = -deltaX;
+      deltaY = -deltaY;
+    }
     if (event._hasInitWheelEvent) {
       var modifiers = [];
       if (ctrlKey) {
@@ -26514,7 +26519,7 @@ class WheelEvent extends MouseEvent native "*WheelEvent" {
       return this._deltaY;
     } else if (JS('bool', '#.wheelDelta !== undefined', this)) {
       // Chrome and IE
-      return this._wheelDelta;
+      return -this._wheelDelta;
     } else if (JS('bool', '#.detail !== undefined', this)) {
       // Firefox
 
@@ -26525,9 +26530,9 @@ class WheelEvent extends MouseEvent native "*WheelEvent" {
         // Firefox is normally the number of lines to scale (normally 3)
         // so multiply it by 40 to get pixels to move, matching IE & WebKit.
         if (detail < 100) {
-          return detail * 40;
+          return -detail * 40;
         }
-        return detail;
+        return -detail;
       }
       return 0;
     }
@@ -26542,7 +26547,7 @@ class WheelEvent extends MouseEvent native "*WheelEvent" {
       return this._deltaX;
     } else if (JS('bool', '#.wheelDeltaX !== undefined', this)) {
       // Chrome
-      return this._wheelDeltaX;
+      return -this._wheelDeltaX;
     } else if (JS('bool', '#.detail !== undefined', this)) {
       // Firefox and IE.
       // IE will have detail set but will not set axis.
@@ -26555,9 +26560,9 @@ class WheelEvent extends MouseEvent native "*WheelEvent" {
         // Firefox is normally the number of lines to scale (normally 3)
         // so multiply it by 40 to get pixels to move, matching IE & WebKit.
         if (detail < 100) {
-          return detail * 40;
+          return -detail * 40;
         }
-        return detail;
+        return -detail;
       }
       return 0;
     }