Make all the files mapped in when running unit_tests read only on Linux and OSX.

This means no file can be opened for write during the test run.

Windows can't be done at the moment due to bug 342913.

R=vadimsh@chromium.org
BUG=116251
BUG=342913

Review URL: https://codereview.chromium.org/136973003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251054 0039d316-1c4b-4281-b951-d872f2087c98

chrome/unit_tests.isolate

@@ -73,6 +73,12 @@
         ],
       },
     }],
+    ['OS=="linux" or OS=="mac"', {
+      'variables': {
+        # Can't be enabled on Windows due to http://crbug.com/342913
+        'read_only': 1,
+      },
+    }],
     ['OS=="mac"', {
       'variables': {
         'isolate_dependency_tracked': [