Make converting from NativeViewId to NativeView an error on Mac.

base/gfx/native_widget_types.h

 // Copyright (c) 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.
 
 #ifndef BASE_GFX_NATIVE_WIDGET_TYPES_H_
 #define BASE_GFX_NATIVE_WIDGET_TYPES_H_
 
 #include "base/basictypes.h"
 #include "build/build_config.h"
 
@@ skipping 71 matching lines @@
 // you make it a type which is smaller than a pointer, you have to fix
 // test_shell.
 //
 // See comment at the top of the file for usage.
 typedef intptr_t NativeViewId;
 
 // Convert a NativeViewId to a NativeView.
 // On Windows, these are both HWNDS so it's just a cast.
 // On Mac, for now, we pass the NSView pointer into the renderer
 // On Linux we use an opaque id
-#if defined(OS_WIN) || defined(OS_MACOSX)
+#if defined(OS_WIN)
 static inline NativeView NativeViewFromId(NativeViewId id) {
   return reinterpret_cast<NativeView>(id);
 }
+#elif defined(OS_MACOSX)
+
+// A recent CL removed the need for Mac to actually convert
+// NativeViewId to NativeView.  Until other platforms make changes,
+// the platform-independent code cannot be removed.  The following is
+// to discourage new platform-independent uses.
+
+#define NativeViewFromId(x) NATIVE_VIEW_FROM_ID_NOT_AVAILABLE_ON_MAC
+
 #elif defined(OS_LINUX)
 // A NativeView on Linux is a GtkWidget*. However, we can't go directly from an
 // X window ID to a GtkWidget. Thus, functions which handle NativeViewIds from
 // the renderer have to use Xlib. This is fine since these functions are
 // generally performed on the BACKGROUND_X thread which can't use GTK anyway.
 
 #define NativeViewFromId(x) NATIVE_VIEW_FROM_ID_NOT_AVAILIBLE_ON_LINUX
 
 #endif  // defined(OS_LINUX)
 
@@ skipping 19 matching lines @@
 #else
   // On OS X we don't have windowed plugins.
   // We use a NULL/0 PluginWindowHandle in shared code to indicate there
   // is no window present, so mirror that behavior here.
   typedef bool PluginWindowHandle;
 #endif
 
 }  // namespace gfx
 
 #endif  // BASE_GFX_NATIVE_WIDGET_TYPES_H_