Had to move this one out to a scoped_ptr too, otherwise when
it's instantiated in test code on the stack,
d:\src\crashpad\crashpad\minidump\minidump_simple_string_dictionary_writer_test.cc(45) : warning C4815: 'dictionary_writer' : zero-sized array in stack object will have no elements (unless the object is an aggregate that has been aggregate initialized)
R=mark@chromium.org
BUG=crashpad:1
Review URL: https://codereview.chromium.org/895313004