Pick up changes from pprof's copy of profile.proto

PiperOrigin-RevId: 669350670
Change-Id: I8b37df0045f2261d5c1c962501f6a6b225378884

tcmalloc/internal/profile.proto

@@ -93,6 +93,12 @@ message Profile {
   // Index into the string table of the type of the preferred sample
   // value. If unset, clients should default to the last sample value.
   int64 default_sample_type = 14;
+  // Documentation link for this profile. The URL must be absolute,
+  // e.g., http://pprof.example.com/cpu-profile.html
+  //
+  // The URL may be missing if the profile was generated by older code or code
+  // that did not bother to supply a link.
+  int64 doc_url = 15;  // Index into string table.
 }
 
 // ValueType describes the semantics and measurement units of a value.