Harden allocator for file-backed memory.

base/metrics/persistent_histogram_allocator.cc

Index: base/metrics/persistent_histogram_allocator.cc
diff --git a/base/metrics/persistent_histogram_allocator.cc b/base/metrics/persistent_histogram_allocator.cc
index 939174ecaf63f867fbfe96bc9b784ba4a6ad0612..a0e38716161934184fb79ca1e8bc94c38646f655 100644
--- a/base/metrics/persistent_histogram_allocator.cc
+++ b/base/metrics/persistent_histogram_allocator.cc
@@ -905,6 +905,8 @@ bool GlobalHistogramAllocator::WriteToPersistentLocation() {
 }
 
 void GlobalHistogramAllocator::DeletePersistentLocation() {
+  memory_allocator()->SetMemoryState(PersistentMemoryAllocator::MEMORY_DELETED);
+
 #if defined(OS_NACL)
   NOTREACHED();
 #else