Support persistent system profiles.

base/metrics/persistent_memory_allocator.cc

Index: base/metrics/persistent_memory_allocator.cc
diff --git a/base/metrics/persistent_memory_allocator.cc b/base/metrics/persistent_memory_allocator.cc
index deb82ac1dbe28aa26d14ee98f48139b3068b3488..f569efa5fd353d9ea18141202a130091129665cd 100644
--- a/base/metrics/persistent_memory_allocator.cc
+++ b/base/metrics/persistent_memory_allocator.cc
@@ -162,6 +162,11 @@ void PersistentMemoryAllocator::Iterator::Reset() {
 }
 
 void PersistentMemoryAllocator::Iterator::Reset(Reference starting_after) {
+  if (starting_after == 0) {
+    Reset();
+    return;
+  }
+
   last_record_.store(starting_after, std::memory_order_relaxed);
   record_count_.store(0, std::memory_order_relaxed);