Make all the files mapped in when running net_unittests read only.

net/net_unittests.isolate

 # Copyright 2014 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.
 {
   'conditions': [
     ['OS=="android" or OS=="linux" or OS=="mac" or OS=="win"', {
       'variables': {
         'isolate_dependency_tracked': [
           '../chrome/test/data/animate1.gif',
           '../chrome/test/data/server-unavailable.html',
@@ skipping 18 matching lines @@
           '<(PRODUCT_DIR)/net_unittests<(EXECUTABLE_SUFFIX)',
         ],
         'isolate_dependency_untracked': [
           '../third_party/pyftpdlib/',
           '../third_party/pywebsocket/',
           '../third_party/tlslite/',
           '../tools/swarming_client/',
           '<(PRODUCT_DIR)/pyproto/',
           'tools/testserver/',
         ],
+        'read_only': 1,
       },
     }],
     ['OS=="linux" and component=="shared_library"', {
       'variables': {
         'isolate_dependency_tracked': [
           '<(PRODUCT_DIR)/lib/libopenssl.so',
         ],
       },
     }],
   ],
   'includes': [
     'net.isolate',
   ],
 }