gpu: Bind dummy GL API when no context is current

ui/gl/gl_context_osmesa.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_context_osmesa.h"
 
 #include <GL/osmesa.h>
 
 #include "base/logging.h"
 #include "ui/gfx/size.h"
@@ skipping 34 matching lines @@
     OSMesaDestroyContext(static_cast<OSMesaContext>(context_));
     context_ = NULL;
   }
 }
 
 bool GLContextOSMesa::MakeCurrent(GLSurface* surface) {
   DCHECK(context_);
 
   gfx::Size size = surface->GetSize();
 
+  ScopedReleaseCurrent release_current;
   if (!OSMesaMakeCurrent(context_,
                          surface->GetHandle(),
                          GL_UNSIGNED_BYTE,
                          size.width(),
                          size.height())) {
     LOG(ERROR) << "OSMesaMakeCurrent failed.";
     Destroy();
     return false;
   }
 
   // Set this as soon as the context is current, since we might call into GL.
   SetRealGLApi();
 
   // Row 0 is at the top.
   OSMesaPixelStore(OSMESA_Y_UP, 0);
 
   SetCurrent(surface);
   if (!InitializeDynamicBindings()) {
-    ReleaseCurrent(surface);
     return false;
   }
 
   if (!surface->OnMakeCurrent(this)) {
     LOG(ERROR) << "Could not make current.";
     return false;
   }
 
+  release_current.Cancel();
   return true;
 }
 
 void GLContextOSMesa::ReleaseCurrent(GLSurface* surface) {
   if (!IsCurrent(surface))
     return;
 
   SetCurrent(NULL);
+  // TODO: Calling with NULL here does not work to release the context.
   OSMesaMakeCurrent(NULL, NULL, GL_UNSIGNED_BYTE, 0, 0);
 }
 
 bool GLContextOSMesa::IsCurrent(GLSurface* surface) {
   DCHECK(context_);
 
   bool native_context_is_current =
       context_ == OSMesaGetCurrentContext();
 
   // If our context is current then our notion of which GLContext is
@@ skipping 23 matching lines @@
 
 void GLContextOSMesa::SetSwapInterval(int interval) {
   DCHECK(IsCurrent(NULL));
 }
 
 GLContextOSMesa::~GLContextOSMesa() {
   Destroy();
 }
 
 }  // namespace gfx