Add ciphers option to bssl.

This simply converts a cipher suite string to the list of cipher suites
that it implies.

Change-Id: Id8b31086715d619ea6601c40a6eb84dc0d8c500d
Reviewed-on: https://boringssl-review.googlesource.com/6370
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/tool/tool.cc b/tool/tool.cc
index f67f0c7..afe6840 100644
--- a/tool/tool.cc
+++ b/tool/tool.cc
@@ -27,6 +27,7 @@
 #endif
 
 
+bool Ciphers(const std::vector<std::string> &args);
 bool Client(const std::vector<std::string> &args);
 bool DoPKCS12(const std::vector<std::string> &args);
 bool GenerateRSAKey(const std::vector<std::string> &args);
@@ -48,6 +49,7 @@
 };
 
 static const Tool kTools[] = {
+  { "ciphers", Ciphers },
   { "client", Client },
   { "genrsa", GenerateRSAKey },
   { "md5sum", MD5Sum },