command_buffer: Avoid glGetError after lost context

gpu/command_buffer/service/gles2_cmd_decoder.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.cc b/gpu/command_buffer/service/gles2_cmd_decoder.cc
index c9e8470b6cca2e031b61a22bbd12e737b48a5c55..549a8e422d7b29a134e713587dce998c4c952653 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -4473,7 +4473,7 @@ error::Error GLES2DecoderImpl::DoCommandsImpl(unsigned int num_commands,
         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() << "] "