Clarify that BlockSizeForFileType can't be called with EXTERNAL FileType

net/disk_cache/blockfile/addr.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This is an internal class that handles the address of a cache record.
 // See net/disk_cache/disk_cache.h for the public interface of the cache.
 
 #ifndef NET_DISK_CACHE_BLOCKFILE_ADDR_H_
 #define NET_DISK_CACHE_BLOCKFILE_ADDR_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
+#include "base/logging.h"
 #include "net/base/net_export.h"
 #include "net/disk_cache/blockfile/disk_format_base.h"
 
 namespace disk_cache {
 
 enum FileType {
   EXTERNAL = 0,
   RANKINGS = 1,
   BLOCK_256 = 2,
   BLOCK_1K = 3,
@@ skipping 107 matching lines @@
       case BLOCK_1K:
         return 1024;
       case BLOCK_4K:
         return 4096;
       case BLOCK_FILES:
         return 8;
       case BLOCK_ENTRIES:
         return 104;
       case BLOCK_EVICTED:
         return 48;
-      default:
+      case EXTERNAL:
+        NOTREACHED();
         return 0;
     }
+    return 0;
   }
 
   static FileType RequiredFileType(int size) {
     if (size < 1024)
       return BLOCK_256;
     else if (size < 4096)
       return BLOCK_1K;
     else if (size <= 4096 * 4)
       return BLOCK_4K;
     else
@@ skipping 23 matching lines @@
   static const uint32_t kFileSelectorOffset = 16;
   static const uint32_t kStartBlockMask = 0x0000FFFF;
   static const uint32_t kFileNameMask = 0x0FFFFFFF;
 
   CacheAddr value_;
 };
 
 }  // namespace disk_cache
 
 #endif  // NET_DISK_CACHE_BLOCKFILE_ADDR_H_