Add link to SPIs.

webkit/glue/webcursor_mac.mm

 // Copyright (c) 2011 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 "webkit/glue/webcursor.h"
 
 #import <AppKit/AppKit.h>
 #include <Carbon/Carbon.h>
 
 #include "base/logging.h"
@@ skipping 93 matching lines @@
   NSCursor* cursor = [[NSCursor alloc] initWithImage:cursor_image
                                              hotSpot:NSMakePoint(hotspot.x(),
                                                                  hotspot.y())];
   [cursor_image release];
 
   return [cursor autorelease];
 }
 
 }  // namespace
 
-// We're matching Safari's cursor choices; see platform/mac/CursorMac.mm
+// We're (mostly) matching Safari's cursor choices; see
+// platform/mac/CursorMac.mm . Note that Safari uses some magic in wkCursor to
+// access private system cursors. A sample implementation using the same
+// technique can be found attached to http://crbug.com/92892 . However, it's not
+// clear that accessing system cursors this way is enough of a gain to risk
+// using SPIs. Until the benefits more clearly outweigh the risks, API is all
+// that will be used.
 NSCursor* WebCursor::GetCursor() const {
   switch (type_) {
     case WebCursorInfo::TypePointer:
       return [NSCursor arrowCursor];
     case WebCursorInfo::TypeCross:
       return [NSCursor crosshairCursor];
     case WebCursorInfo::TypeHand:
       // If >= 10.7, the pointingHandCursor has a shadow so use it. Otherwise
       // use the custom one.
       if (base::mac::IsOSLionOrLater())
@@ skipping 341 matching lines @@
   return true;
 }
 
 void WebCursor::CleanupPlatformData() {
   return;
 }
 
 void WebCursor::CopyPlatformData(const WebCursor& other) {
   return;
 }