Linux: Fix some NULL versus 0 issues to appease gcc-4.5.

app/gfx/gl/gl_context_linux.cc

 // Copyright (c) 2010 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.
 
 // This file implements the ViewGLContext and PbufferGLContext classes.
 
 #include "app/gfx/gl/gl_context.h"
 
 #include <GL/osmesa.h>
 
@@ skipping 300 matching lines @@
 
   Display* display = x11_util::GetXDisplay();
 
   if (pixmap_graphics_context_) {
     XFreeGC(display, pixmap_graphics_context_);
     pixmap_graphics_context_ = NULL;
   }
 
   if (pixmap_) {
     XFreePixmap(display, pixmap_);
-    pixmap_ = NULL;
+    pixmap_ = 0;
   }
 
   if (window_graphics_context_) {
     XFreeGC(display, window_graphics_context_);
     window_graphics_context_ = NULL;
   }
 }
 
 bool OSMesaViewGLContext::MakeCurrent() {
   // TODO(apatrick): This is a bit of a hack. The window might have had zero
@@ skipping 67 matching lines @@
   // Change osmesa surface size to that of window.
   osmesa_context_.Resize(window_size);
 
   // Destroy the previous pixmap and graphics context.
   if (pixmap_graphics_context_) {
     XFreeGC(display, pixmap_graphics_context_);
     pixmap_graphics_context_ = NULL;
   }
   if (pixmap_) {
     XFreePixmap(display, pixmap_);
-    pixmap_ = NULL;
+    pixmap_ = 0;
   }
 
   // Recreate a pixmap to hold the frame.
   pixmap_ = XCreatePixmap(display,
                           window_,
                           window_size.width(),
                           window_size.height(),
                           attributes.depth);
   if (!pixmap_) {
     LOG(ERROR) << "XCreatePixmap failed.";
@@ skipping 314 matching lines @@
     }
     case kGLImplementationMockGL:
       return new StubGLContext;
     default:
       NOTREACHED();
       return NULL;
   }
 }
 
 }  // namespace gfx