Fix crash in screen capturer on Mac

BUG=crbug.com/247685
R=wez@chromium.org

Review URL: https://webrtc-codereview.appspot.com/2006004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@4518 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/modules/desktop_capture/screen_capturer_mac.mm

@@ -463,7 +463,7 @@ void ScreenCapturerMac::GlBlitFast(const DesktopFrame& frame,
 
     // Since the image obtained from OpenGL is upside-down, need to do some
     // magic here to copy the correct rectangle.
-    const int y_offset = (frame.size().width() - 1) * frame.stride();
+    const int y_offset = (frame.size().height() - 1) * frame.stride();
     for (DesktopRegion::Iterator i(last_invalid_region_);
          !i.IsAtEnd(); i.Advance()) {
       DesktopRect copy_rect = i.rect();