Fix a few warnings that -Wnull-conversion of a future clang will complain about.

content/renderer/webplugin_delegate_proxy.cc

 // 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 "content/renderer/webplugin_delegate_proxy.h"
 
 #if defined(TOOLKIT_USES_GTK)
 #include <gtk/gtk.h>
 #elif defined(USE_X11)
 #include <cairo/cairo.h>
@@ skipping 1299 matching lines @@
 void WebPluginDelegateProxy::OnBindFakePluginWindowHandle(bool opaque) {
   BindFakePluginWindowHandle(opaque);
 }
 
 // Synthesize a fake window handle for the plug-in to identify the instance
 // to the browser, allowing mapping to a surface for hardware acceleration
 // of plug-in content. The browser generates the handle which is then set on
 // the plug-in. Returns true if it successfully sets the window handle on the
 // plug-in.
 bool WebPluginDelegateProxy::BindFakePluginWindowHandle(bool opaque) {
-  gfx::PluginWindowHandle fake_window = NULL;
+  gfx::PluginWindowHandle fake_window = gfx::kNullPluginWindow;
   if (render_view_)
     fake_window = render_view_->AllocateFakePluginWindowHandle(opaque, false);
   // If we aren't running on 10.6, this allocation will fail.
   if (!fake_window)
     return false;
   OnSetWindow(fake_window);
   if (!Send(new PluginMsg_SetFakeAcceleratedSurfaceWindowHandle(instance_id_,
                                                                 fake_window))) {
     return false;
   }
@@ skipping 77 matching lines @@
 }
 
 void WebPluginDelegateProxy::OnAcceleratedSurfaceBuffersSwapped(
     gfx::PluginWindowHandle window, uint64 surface_handle) {
   if (render_view_)
     render_view_->AcceleratedSurfaceBuffersSwapped(window, surface_handle);
 }
 
 void WebPluginDelegateProxy::OnAcceleratedPluginEnabledRendering() {
   uses_compositor_ = true;
-  OnSetWindow(NULL);
+  OnSetWindow(gfx::kNullPluginWindow);
 }
 
 void WebPluginDelegateProxy::OnAcceleratedPluginAllocatedIOSurface(
     int32 width,
     int32 height,
     uint32 surface_id) {
   if (plugin_)
     plugin_->AcceleratedPluginAllocatedIOSurface(width, height, surface_id);
 }
 
@@ skipping 27 matching lines @@
 }
 #endif
 
 void WebPluginDelegateProxy::OnURLRedirectResponse(bool allow,
                                                    int resource_id) {
   if (!plugin_)
     return;
 
   plugin_->URLRedirectResponse(allow, resource_id);
 }