Add RandomString() and its test, and use it everywhere it makes sense

util/util.gyp

 # Copyright 2014 The Crashpad Authors. All rights reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
 # You may obtain a copy of the License at
 #
 #     http://www.apache.org/licenses/LICENSE-2.0
 #
 # Unless required by applicable law or agreed to in writing, software
 # distributed under the License is distributed on an "AS IS" BASIS,
@@ skipping 76 matching lines @@
         'misc/clock.h',
         'misc/clock_mac.cc',
         'misc/clock_posix.cc',
         'misc/clock_win.cc',
         'misc/implicit_cast.h',
         'misc/initialization_state.h',
         'misc/initialization_state_dcheck.cc',
         'misc/initialization_state_dcheck.h',
         'misc/pdb_structures.cc',
         'misc/pdb_structures.h',
+        'misc/random_string.cc',
+        'misc/random_string.h',
         'misc/scoped_forbid_return.cc',
         'misc/scoped_forbid_return.h',
         'misc/symbolic_constants_common.h',
         'misc/tri_state.h',
         'misc/uuid.cc',
         'misc/uuid.h',
         'net/http_body.cc',
         'net/http_body.h',
         'net/http_headers.cc',
         'net/http_headers.h',
@@ skipping 156 matching lines @@
                   'UseSafeExceptionHandlers': 'true',
                 },
               },
             }],
           ],
         }],
       ],
     },
   ],
 }