use skia cgimage->bitmap routine

skia/ext/skia_utils_mac.mm

 // 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 "skia/ext/skia_utils_mac.h"
 
 #import <AppKit/AppKit.h>
 #include <stdint.h>
 
 #include <memory>
@@ skipping 166 matching lines @@
     SkColorGetG(color) / 255.0,
     SkColorGetB(color) / 255.0,
     SkColorGetA(color) / 255.0
   };
   return [NSColor colorWithColorSpace:[NSColorSpace sRGBColorSpace]
                            components:components
                                 count:4];
 }
 
 SkBitmap CGImageToSkBitmap(CGImageRef image) {
-  if (!image)
-    return SkBitmap();
-
-  int width = CGImageGetWidth(image);
-  int height = CGImageGetHeight(image);
-
-  std::unique_ptr<SkCanvas> canvas(
-      skia::TryCreateBitmapCanvas(width, height, false));
-  ScopedPlatformPaint p(canvas.get());
-  CGContextRef context = p.GetNativeDrawingContext();
-
-  // We need to invert the y-axis of the canvas so that Core Graphics drawing
-  // happens right-side up. Skia has an upper-left origin and CG has a lower-
-  // left one.
-  CGContextScaleCTM(context, 1.0, -1.0);
-  CGContextTranslateCTM(context, 0, -height);
-
-  // We want to copy transparent pixels from |image|, instead of blending it
-  // onto uninitialized pixels.
-  CGContextSetBlendMode(context, kCGBlendModeCopy);
-
-  CGRect rect = CGRectMake(0, 0, width, height);
-  CGContextDrawImage(context, rect, image);
-
-  return skia::ReadPixels(canvas.get());
+  SkBitmap bitmap;
+  if (image && SkCreateBitmapFromCGImage(&bitmap, image))
+    return bitmap;
+  return SkBitmap();
 }
 
 SkBitmap NSImageToSkBitmapWithColorSpace(
     NSImage* image, bool is_opaque, CGColorSpaceRef color_space) {
   return NSImageOrNSImageRepToSkBitmapWithColorSpace(
       image, nil, [image size], is_opaque, color_space);
 }
 
 SkBitmap NSImageRepToSkBitmapWithColorSpace(NSImageRep* image_rep,
                                             NSSize size,
@@ skipping 156 matching lines @@
   CGContextConcatCTM(cgContext_, SkMatrixToCGAffineTransform(matrix));
   
   return cgContext_;
 }
 
 bool SkiaBitLocker::hasEmptyClipRegion() const {
   return canvas_->isClipEmpty();
 }
 
 }  // namespace skia