Remove PostFile() from session; refine cmake files; replace final with override.

webcc/utility.h

@@ -7,6 +7,10 @@ namespace webcc {
 
 std::string RandomUuid();
 
+// Split a string to two parts by the given token.
+bool Split2(const std::string& str, char token, std::string* part1,
+            std::string* part2);
+
 }  // namespace webcc
 
 #endif  // WEBCC_UTILITY_H_