Add swapBuffer call to SkGLContextHelper.

src/gpu/gl/unix/SkNativeGLContext_unix.cpp

 
 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #include "gl/SkNativeGLContext.h"
 
 #include <GL/glu.h>
@@ skipping 267 matching lines @@
         return NULL;
     }
     return interface;
 }
 
 void SkNativeGLContext::makeCurrent() const {
     if (!glXMakeCurrent(fDisplay, fGlxPixmap, fContext)) {
         SkDebugf("Could not set the context.\n");
     }
 }
+
+void SkNativeGLContext::swapBuffers() const {
+    glXSwapBuffers(fDisplay, fGlxPixmap);
+}