Fix PartitionAlloc cookies for large in-place reallocs

base/allocator/partition_allocator/partition_alloc.cc

Index: base/allocator/partition_allocator/partition_alloc.cc
diff --git a/base/allocator/partition_allocator/partition_alloc.cc b/base/allocator/partition_allocator/partition_alloc.cc
index 439ce177d88a5061ce42e50b50b94f8f0a923a1e..b13f36bb530265099b5bb31cbe0918a73450a98a 100644
--- a/base/allocator/partition_allocator/partition_alloc.cc
+++ b/base/allocator/partition_allocator/partition_alloc.cc
@@ -1051,8 +1051,13 @@ void* PartitionReallocGeneric(PartitionRootGeneric* root,
   // determine it is a win.
   if (actual_new_size == actual_old_size) {
     // Trying to allocate a block of size new_size would give us a block of
-    // the same size as the one we've already got, so no point in doing
-    // anything here.
+    // the same size as the one we've already got, so re-use the allocation
+    // after updating statistics (and cookies, if present).
+    PartitionPageSetRawSize(page, PartitionCookieSizeAdjustAdd(new_size));
+#if DCHECK_IS_ON()
+    // Write a new trailing cookie.
+    PartitionCookieWriteValue(static_cast<char*>(ptr) + new_size);
+#endif
     return ptr;
   }