Merge pull request #15235 from huchengtw-moz/gallery/Bug_951241-blue-…

…line

Bug 951241 - [B2G][Gallery][Image Edit] Image preview in edit mode shows...,  r=djf

apps/gallery/js/ImageEditor.js

@@ -547,7 +547,10 @@ ImageEditor.prototype.generateNewPreview = function(callback) {
   var canvas = document.createElement('canvas');
   canvas.width = previewWidth;
   canvas.height = previewHeight;
-  var context = canvas.getContext('2d');
+  // In this case, we only need graphic 2d to do the scaling. The
+  // willReadFrequently option makes canvas use software graphic 2d. This can
+  // skip a bug of GPU version, bug 960276.
+  var context = canvas.getContext('2d', { willReadFrequently: true });
 
   // Draw that region of the image into the canvas, scaling it down
   context.drawImage(this.original, this.source.x, this.source.y,