Add a version of gpu_fuzzer that is backed by the NULL ANGLE backend

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 986dbba7e3603d696fabe1ac235414e38671b435..68cdf5bd942ba98fb8033dc83e789ba38424c7ec 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -4803,6 +4803,10 @@ void GLES2DecoderImpl::Destroy(bool have_context) {
   offscreen_resolved_frame_buffer_.reset();
   offscreen_resolved_color_texture_.reset();
 
+  // Release all fences now, because some fence types need the context to be
+  // current on destruction.
+  pending_readpixel_fences_ = std::queue<FenceCallback>();
+
   // Need to release these before releasing |group_| which may own the
   // ShaderTranslatorCache.
   fragment_translator_ = NULL;