[Mojo] Fix race condition in sample_app's SwapBuffers

mojo/services/gles2/gles2_impl.cc

 // Copyright 2013 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 "mojo/services/gles2/gles2_impl.h"
 
 #include "base/bind.h"
 #include "gpu/command_buffer/client/gl_in_process_context.h"
 #include "gpu/command_buffer/client/gles2_implementation.h"
 
 namespace mojo {
 namespace services {
 
 GLES2Impl::GLES2Impl(ScopedMessagePipeHandle client)
     : client_(client.Pass()) {
   client_.SetPeer(this);
 }
 
 GLES2Impl::~GLES2Impl() {
 }
 
-void GLES2Impl::SwapBuffers() {
-  if (!gl_context_)
-    return;
-  gl_context_->GetImplementation()->SwapBuffers();
+void GLES2Impl::Destroy() {
+  gl_context_.reset();
 }
 
 void GLES2Impl::CreateContext(gfx::AcceleratedWidget widget,
                               const gfx::Size& size) {
   gpu::GLInProcessContextAttribs attribs;
   gl_context_.reset(gpu::GLInProcessContext::CreateContext(
       false, widget, size, false, attribs, gfx::PreferDiscreteGpu));
   gl_context_->SetContextLostCallback(base::Bind(
       &GLES2Impl::OnGLContextLost, base::Unretained(this)));
 
   gpu::gles2::GLES2Interface* gl = gl_context_->GetImplementation();
   uint64_t encoded_gl = static_cast<uint64_t>(reinterpret_cast<uintptr_t>(gl));
 
   client_->DidCreateContext(encoded_gl, size.width(), size.height());
 }
 
 void GLES2Impl::OnGLContextLost() {
   client_->ContextLost();
 }
 
 }  // namespace services
 }  // namespace mojo