message: Fix memory leak in `XlaTensorBuffer`.
  My recent change to devirtualize `TensorBuffer::data()` had a bug, in that it continued to use the now-uninitialized `XlaTensorBuffer::data_` field to decide whether to free the buffer.
diff: @@ -205,7 +205,7 @@ class XlaTensorBuffer : public TensorBuffer {
  allocator_(allocator) {}
  ~XlaTensorBuffer() override {
  - if (data_) {
  + if (data()) {
  allocator_->DeallocateRaw(data());
  }
  }
  @@ -229,7 +229,6 @@ class XlaTensorBuffer : public TensorBuffer {
  }
  private:
  - void* data_;
  size_t expected_size_;
  size_t actual_size_;
  Allocator* allocator_;
  