Mark SwapBuffers for an offscreen surface as unimplemented

gpu/command_buffer/service/gles2_cmd_decoder_passthrough_doers.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder_passthrough_doers.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder_passthrough_doers.cc b/gpu/command_buffer/service/gles2_cmd_decoder_passthrough_doers.cc
index db92cb4dda07bee3497fdbda38c24f1fed4cc801..59b9c7af929d31829cb2b661977a250d25cc3f61 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder_passthrough_doers.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder_passthrough_doers.cc
@@ -2463,6 +2463,11 @@ error::Error GLES2DecoderPassthroughImpl::DoBindVertexArrayOES(GLuint array) {
 }
 
 error::Error GLES2DecoderPassthroughImpl::DoSwapBuffers() {
+  if (offscreen_) {
+    NOTIMPLEMENTED();
+    return error::kNoError;
+  }
+
   gfx::SwapResult result = surface_->SwapBuffers();
   if (result == gfx::SwapResult::SWAP_FAILED) {
     LOG(ERROR) << "Context lost because SwapBuffers failed.";