message: Fix linker error for missing constexpr initialization.
diff: @@ -29,12 +29,12 @@ namespace tensorflow {
  namespace {
  -class GrpcWorkerCache : public WorkerCachePartial {
  - public:
  // TODO(ncteisen): consider adding a config var or flag for this
  - static constexpr size_t kGrpcWorkerCacheThreadCount = 8;
  - static constexpr size_t kNumCallbackThreads = 10;
  +static const size_t kGrpcWorkerCacheThreadCount = 8;
  +static const size_t kNumCallbackThreads = 10;
  +class GrpcWorkerCache : public WorkerCachePartial {
  + public:
  explicit GrpcWorkerCache(std::shared_ptr<GrpcChannelCache> channel_cache,
  WorkerInterface* local_worker,
  const string& local_target,
  