Fix bug where custom cursors would dissappear when screen was rotated

ui/gfx/skbitmap_operations.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/gfx/skbitmap_operations.h"
 
 #include <string.h>
 #include <algorithm>
 
 #include "base/logging.h"
@@ skipping 739 matching lines @@
     canvas.restore();
   }
 
   canvas.drawBitmap(bitmap, SkIntToScalar(0), SkIntToScalar(0));
   return image_with_shadow;
 }
 
 // static
 SkBitmap SkBitmapOperations::Rotate(const SkBitmap& source,
                                     RotationAmount rotation) {
+  // SkCanvas::drawBitmap() fails silently with unpremultiplied SkBitmap.
+  DCHECK(source.info().alphaType() != kUnpremul_SkAlphaType);
+
   SkBitmap result;
   SkScalar angle = SkFloatToScalar(0.0f);
 
   switch (rotation) {
    case ROTATION_90_CW:
      angle = SkFloatToScalar(90.0f);
      result.allocN32Pixels(source.height(), source.width());
      break;
    case ROTATION_180_CW:
      angle = SkFloatToScalar(180.0f);
@@ skipping 11 matching lines @@
   canvas.translate(SkFloatToScalar(result.width() * 0.5f),
                    SkFloatToScalar(result.height() * 0.5f));
   canvas.rotate(angle);
   canvas.translate(-SkFloatToScalar(source.width() * 0.5f),
                    -SkFloatToScalar(source.height() * 0.5f));
   canvas.drawBitmap(source, 0, 0);
   canvas.flush();
 
   return result;
 }