Harden allocator for file-backed memory.

components/metrics/file_metrics_provider.cc

Index: components/metrics/file_metrics_provider.cc
diff --git a/components/metrics/file_metrics_provider.cc b/components/metrics/file_metrics_provider.cc
index 24cfa9b761368155ec1698486ceef795f8a89a82..137e9dc895bd47464e8b3727a22eb19ae1a524af 100644
--- a/components/metrics/file_metrics_provider.cc
+++ b/components/metrics/file_metrics_provider.cc
@@ -335,10 +335,18 @@ FileMetricsProvider::AccessResult FileMetricsProvider::CheckAndMapMetricSource(
     return ACCESS_RESULT_INVALID_CONTENTS;
   }
 
-  // Create an allocator for the mapped file. Ownership passes to the allocator.
-  source->allocator.reset(new base::PersistentHistogramAllocator(
+  // Map the file and validate it.
+  std::unique_ptr<base::PersistentMemoryAllocator> memory_allocator =
       base::MakeUnique<base::FilePersistentMemoryAllocator>(
-          std::move(mapped), 0, 0, base::StringPiece(), read_only)));
+          std::move(mapped), 0, 0, base::StringPiece(), read_only);
+  if (memory_allocator->GetMemoryState() ==
+      base::PersistentMemoryAllocator::MEMORY_DELETED) {
+    return ACCESS_RESULT_MEMORY_DELETED;
+  }
+
+  // Create an allocator for the mapped file. Ownership passes to the allocator.
+  source->allocator = base::MakeUnique<base::PersistentHistogramAllocator>(
+      std::move(memory_allocator));
 
   return ACCESS_RESULT_SUCCESS;
 }