Make Join support string delimiters

We've needed this several times in the past.

Change-Id: I7324e8083fe2ff1aa0bf392a8c124fc2f3bb26e2
Test: Full android build
Signed-off-by: Casey Dahlin <sadmac@google.com>
diff --git a/base/strings.cpp b/base/strings.cpp
index bac983b..d687e3c 100644
--- a/base/strings.cpp
+++ b/base/strings.cpp
@@ -83,6 +83,8 @@
 // aid compile time and binary size.
 template std::string Join(const std::vector<std::string>&, char);
 template std::string Join(const std::vector<const char*>&, char);
+template std::string Join(const std::vector<std::string>&, const std::string&);
+template std::string Join(const std::vector<const char*>&, const std::string&);
 
 bool StartsWith(const std::string& s, const char* prefix) {
   return s.compare(0, strlen(prefix), prefix) == 0;