Clean up surface after ContextGroup destruction.

Rather than removing the command decoder's reference to the current
surface before ContextGroup destruction, do so afterwards.  Group
destruction might need the surface.

Bug: 718117
Change-Id: I39edc795a427c89f9a31fbd9d9d5ad58f9de0000
Reviewed-on: https://chromium-review.googlesource.com/574636Reviewed-by: Antoine Labour <piman@chromium.org>
Commit-Queue: Frank Liberato <liberato@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487155}

gpu/command_buffer/service/gles2_cmd_decoder.cc

@@ -4914,15 +4914,15 @@ void GLES2DecoderImpl::Destroy(bool have_context) {
     gpu_tracer_.reset();
   }
 
-  // Destroy the surface before the context, some surface destructors make GL
-  // calls.
-  surface_ = nullptr;
-
   if (group_.get()) {
     group_->Destroy(this, have_context);
     group_ = NULL;
   }
 
+  // Destroy the surface before the context, some surface destructors make GL
+  // calls.
+  surface_ = nullptr;
+
   if (context_.get()) {
     context_->ReleaseCurrent(NULL);
     context_ = NULL;