[NFC][sanitizer] Move StackStore::Allocated into cpp file

GitOrigin-RevId: cdc80a6017076daea28e62a9efb0b3d8a53d8fce
diff --git a/lib/sanitizer_common/sanitizer_stack_store.cpp b/lib/sanitizer_common/sanitizer_stack_store.cpp
index ad88e2b..74be6df 100644
--- a/lib/sanitizer_common/sanitizer_stack_store.cpp
+++ b/lib/sanitizer_common/sanitizer_stack_store.cpp
@@ -31,6 +31,10 @@
   return StackTrace(stack_trace + 1, size, tag);
 }
 
+uptr StackStore::Allocated() const {
+  return atomic_load_relaxed(&mapped_size_);
+}
+
 uptr *StackStore::TryAlloc(uptr count) {
   // Optimisic lock-free allocation, essentially try to bump the region ptr.
   for (;;) {
diff --git a/lib/sanitizer_common/sanitizer_stack_store.h b/lib/sanitizer_common/sanitizer_stack_store.h
index b5bbdcc..35602d2 100644
--- a/lib/sanitizer_common/sanitizer_stack_store.h
+++ b/lib/sanitizer_common/sanitizer_stack_store.h
@@ -24,7 +24,7 @@
 
   Id Store(const StackTrace &trace);
   StackTrace Load(Id id);
-  uptr Allocated() const { return atomic_load_relaxed(&mapped_size_); }
+  uptr Allocated() const;
 
   void TestOnlyUnmap();