command_buffer: Avoid glGetError after lost context

gpu/command_buffer/service/gles2_cmd_decoder.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 "gpu/command_buffer/service/gles2_cmd_decoder.h"
 
 #include <limits.h>
 #include <stddef.h>
 #include <stdint.h>
 #include <stdio.h>
@@ skipping 4455 matching lines @@
         }
 
         uint32_t immediate_data_size = (arg_count - info_arg_count) *
                                        sizeof(CommandBufferEntry);  // NOLINT
 
         result = (this->*info.cmd_handler)(immediate_data_size, cmd_data);
 
         if (DebugImpl && doing_gpu_trace)
           gpu_tracer_->End(kTraceDecoder);
 
-        if (DebugImpl && debug()) {
+        if (DebugImpl && debug() && !WasContextLost()) {

[Zhenyao Mo, 2016/04/26 17:19:39]

I try to understand 

1) what difference does this make?
2) Don't you still want to clear the error from the driver, just not expose them
through log and local_set_gl_error?

[Kimmo Kinnunen, 2016/04/26 18:09:23]

I was thinking more in terms of:
After the context is lost, you can not make the context current anymore.
If you do not have the context current, you are not allowed to call a gl
function.
glGetError is a gl function.

If you have debugging on and have context lost, it will call glGetError without
the correct context.

           GLenum error;
           while ((error = glGetError()) != GL_NO_ERROR) {
             LOG(ERROR) << "[" << logger_.GetLogPrefix() << "] "
                        << "GL ERROR: " << GLES2Util::GetStringEnum(error)
                        << " : " << GetCommandName(command);
             LOCAL_SET_GL_ERROR(error, "DoCommand", "GL error from driver");
           }
         }
       } else {
         result = error::kInvalidArguments;
@@ skipping 11870 matching lines @@
 }
 
 // Include the auto-generated part of this file. We split this because it means
 // we can easily edit the non-auto generated parts right here in this file
 // instead of having to edit some template or the code generator.
 #include "base/macros.h"
 #include "gpu/command_buffer/service/gles2_cmd_decoder_autogen.h"
 
 }  // namespace gles2
 }  // namespace gpu