Fix segfault.

Make xla::MemorySpaceDescription back its own pointers. Also, add missing
reserve() so memory_description_pointers don't go uninitialized.

PiperOrigin-RevId: 708047563

xla/pjrt/pjrt_c_api_client.cc

@@ -1030,6 +1030,7 @@ PjRtCApiDeviceDescription::memory_spaces() const {
         extension->PJRT_DeviceDescription_MemoryDescriptions(&mem_desc_args),
         c_api_);
 
+    memory_space_descriptions_.reserve(mem_desc_args.num_memory_descriptions);
     for (int i = 0; i < mem_desc_args.num_memory_descriptions; i++) {
       PJRT_MemoryDescription_Kind_Args kind_args;
       kind_args.struct_size = PJRT_MemoryDescription_Kind_Args_STRUCT_SIZE,

xla/pjrt/pjrt_device_description.h

@@ -36,15 +36,15 @@ class PjRtMemorySpaceDescription {
 
   // A platform-dependent string that uniquely identifies the kind of the
   // memory space.
-  absl::string_view kind() const { return kind_; }
+  absl::string_view kind() const { return absl::string_view(kind_); }
 
   // An ID uniquely identifies the kind of the memory space among those attached
   // to the same `PjRtClient`. The IDs assigned to a kind is implementation
   // specific.
   int kind_id() const { return kind_id_; }
 
  private:
-  absl::string_view kind_;
+  std::string kind_;
   int kind_id_;
 };