Created by: chenwhql

DebugString interface is used in GLOG for printing log, This PR add SelectedRows parse code in DebugString for selected support work later.

original:

I1127 11:24:20.558859 29918 layer.cc:321] Op(lookup_table_grad): Inputs: Ids{_generated_var_0[LoDTensor<int64_t, CUDAPlace(0), (4, 3, 1)>]}, Out@GRAD{tmp_0@GRAD[LoDTensor<float, CUDAPlace(0), (4, 3, 10)>]}, W{simple_net/SimpleNet_0/Embedding_0.embedding_para[LoDTensor<NOT_INITED>]}, Outputs: W@GRAD{Gtmp@[UNRESOLVED_TYPE]}

new:

I1128 04:17:59.010835 26518 layer.cc:337] Op(lookup_table_grad): Inputs: Ids{_generated_var_0[LoDTensor<int64_t, CUDAPlace(0), (4, 3, 1)>]}, Out@GRAD{tmp_0@GRAD[LoDTensor<float, CUDAPlace(0), (4, 3, 10)>]}, W{simple_net/SimpleNet_0/Embedding_0.embedding_para[LoDTensor<NOT_INITED>]}, Outputs: W@GRAD{Gtmp@[SelectedRows<float, CUDAPlace(0), height(1000), rows(0 1 2 3 4 5 6 7 8 9 10 11 ), dims(12, 10)>]}