gpu: Fix corrupted state due to virtual MakeCurrent race.

ui/gl/gl_gl_api_implementation.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 "ui/gl/gl_gl_api_implementation.h"
 
 #include <algorithm>
 #include <vector>
 
 #include "base/command_line.h"
@@ skipping 233 matching lines @@
   // based on GL_ARB_occlusion_query without a lot of work virtualizing
   // queries.
   it = std::find(ext.begin(), ext.end(), "GL_EXT_occlusion_query_boolean");
   if (it != ext.end())
     ext.erase(it);
 
   extensions_ = JoinString(ext, " ");
 }
 
 bool VirtualGLApi::MakeCurrent(GLContext* virtual_context, GLSurface* surface) {
+  DCHECK_EQ(!virtual_context, !surface);
+  if (!virtual_context && !surface) {
+    current_context_ = NULL;
+    return true;
+  }
+
   bool switched_contexts = g_current_gl_context != this;
   GLSurface* current_surface = GLSurface::GetCurrent();
   if (switched_contexts || surface != current_surface) {
     if (!switched_contexts && current_surface &&
         virtual_context->IsCurrent(surface)) {
       // MakeCurrent 'lite' path that avoids potentially expensive MakeCurrent()
       // calls if the GLSurface uses the same underlying surface or renders to
       // an FBO.
       if (!surface->OnMakeCurrent(real_context_)) {
         LOG(ERROR) << "Could not make GLSurface current.";
@@ skipping 36 matching lines @@
 const GLubyte* VirtualGLApi::glGetStringFn(GLenum name) {
   switch (name) {
     case GL_EXTENSIONS:
       return reinterpret_cast<const GLubyte*>(extensions_.c_str());
     default:
       return driver_->fn.glGetStringFn(name);
   }
 }
 
 }  // namespace gfx