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

util/misc/random_string.h

Index: util/misc/random_string.h
diff --git a/handler/handler_main.h b/util/misc/random_string.h
similarity index 63%
copy from handler/handler_main.h
copy to util/misc/random_string.h
index 5b5568ecde6085e7f5ec680a8e0ec85d80964547..93b3a7fa4620f149529c8af1e9b067b9a81ca4a4 100644
--- a/handler/handler_main.h
+++ b/util/misc/random_string.h
@@ -12,17 +12,20 @@
 // 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_