Add a SafeMap equivalent to std::map but without the error-prone operator[].

Change-Id: Iae5ba2091c55a34dbd1005cf3d25fce2a8d5c1f9
diff --git a/src/zip_archive.h b/src/zip_archive.h
index 4f95284..3889fcb 100644
--- a/src/zip_archive.h
+++ b/src/zip_archive.h
@@ -21,12 +21,11 @@
 #include <sys/mman.h>
 #include <zlib.h>
 
-#include <map>
-
 #include "file.h"
 #include "globals.h"
 #include "logging.h"
 #include "mem_map.h"
+#include "safe_map.h"
 #include "stringpiece.h"
 #include "UniquePtr.h"
 
@@ -120,7 +119,7 @@
   uint16_t num_entries_;
   off_t dir_offset_;
   UniquePtr<MemMap> dir_map_;
-  typedef std::map<StringPiece, const byte*> DirEntries;
+  typedef SafeMap<StringPiece, const byte*> DirEntries;
   DirEntries dir_entries_;
 
   friend class ZipEntry;