[sql] Remove mmap before Raze().

sql/connection.cc

Index: sql/connection.cc
diff --git a/sql/connection.cc b/sql/connection.cc
index 0511e11b5c5b22361bbdf24cc1230203749f272b..c80758f3d6bc102c84794a0c9a4db04d2fad0243 100644
--- a/sql/connection.cc
+++ b/sql/connection.cc
@@ -1112,6 +1112,15 @@ bool Connection::Raze() {
   // page_size" can be used to query such a database.
   ScopedWritableSchema writable_schema(db_);
 
+#if defined(OS_WIN)
+  // On Windows, truncate silently fails when applied to memory-mapped files.
+  // Disable memory-mapping so that the truncate succeeds.  Note that other
+  // connections may have memory-mapped the file, so this may not entirely
+  // prevent the problem.
+  // [Source: <https://sqlite.org/mmap.html> plus experiments.]
+  ignore_result(Execute("PRAGMA mmap_size = 0"));
+#endif
+
   const char* kMain = "main";
   int rc = BackupDatabase(null_db.db_, db_, kMain);
   UMA_HISTOGRAM_SPARSE_SLOWLY("Sqlite.RazeDatabase",rc);