A null CGImageRef should be treated as a "null" SkBitmap,...

skia/ext/skia_utils_mac.mm

 // Copyright (c) 2006-2008 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 "base/logging.h"
 #include "base/scoped_cftyperef.h"
@@ skipping 66 matching lines @@
 
 // Converts ARGB to CGColorRef.
 CGColorRef SkColorToCGColorRef(SkColor color) {
   return CGColorCreateGenericRGB(SkColorGetR(color) / 255.0,
                                  SkColorGetG(color) / 255.0,
                                  SkColorGetB(color) / 255.0,
                                  SkColorGetA(color) / 255.0);
 }
 
 SkBitmap CGImageToSkBitmap(CGImageRef image) {
-  DCHECK(image != NULL);
+  if (!image)
+    return SkBitmap();
 
   int width = CGImageGetWidth(image);
   int height = CGImageGetHeight(image);
 
   scoped_ptr<skia::BitmapPlatformDevice> device(
       skia::BitmapPlatformDevice::Create(NULL, width, height, false));
 
   CGContextRef context = device->GetBitmapContext();
 
   // We need to invert the y-axis of the canvas so that Core Graphics drawing
@@ skipping 75 matching lines @@
   // Now convert to NSImage.
   NSBitmapImageRep* bitmap = [[[NSBitmapImageRep alloc]
                                    initWithCGImage:cgimage] autorelease];
   CFRelease(cgimage);
   NSImage* image = [[[NSImage alloc] init] autorelease];
   [image addRepresentation:bitmap];
   return image;
 }
 
 }  // namespace gfx