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

util/misc/random_string.h

 // Copyright 2015 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,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-#ifndef CRASHPAD_HANDLER_HANDLER_MAIN_H_
-#define CRASHPAD_HANDLER_HANDLER_MAIN_H_
+#ifndef CRASHPAD_UTIL_MISC_RANDOM_STRING_H_
+#define CRASHPAD_UTIL_MISC_RANDOM_STRING_H_
+
+#include <string>
 
 namespace crashpad {
 
-//! \brief The `main()` of the `crashpad_handler` binary.
+//! \brief Returns a random string.
 //!
-//! This is exposed so that `crashpad_handler` can be embedded into another
-//! binary, but called and used as if it were a standalone executable.
-int HandlerMain(int argc, char* argv[]);
+//! The string consists of 16 uppercase characters chosen at random. The
+//! returned string has over 75 bits of randomness (26<sup>16</sup> &gt;
+//! 2<sup>75</sup>).
+std::string RandomString();
 
 }  // namespace crashpad
 
-#endif  // CRASHPAD_HANDLER_HANDLER_MAIN_H_
+#endif  // CRASHPAD_UTIL_MISC_RANDOM_STRING_H_