New test and off-by-one fix for data persisted to disk.

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 8b4c4a4cd759758d64623d19e36f1067f24adeb8..839f912a4a382523cad98eddd126b92561f42514 100644
--- a/base/metrics/persistent_memory_allocator.cc
+++ b/base/metrics/persistent_memory_allocator.cc
@@ -274,7 +274,7 @@ size_t PersistentMemoryAllocator::GetAllocSize(Reference ref) const {
   uint32_t size = block->size;
   // Header was verified by GetBlock() but a malicious actor could change
   // the value between there and here. Check it again.
-  if (size <= sizeof(BlockHeader) || ref + size >= mem_size_) {
+  if (size <= sizeof(BlockHeader) || ref + size > mem_size_) {
     SetCorrupt();
     return 0;
   }