Dump INFO CODE_ID containing Build ID in Linux dump_syms

I'd like to have the Build ID available for our symbol server
uploading, and this will make it easy.

Most of this change is me rewriting dump_symbols_unittest to be
typed tests so I could add a new test there.

R=mark@chromium.org
BUG=

Review URL: https://codereview.chromium.org/2052263002 .

src/common/linux/file_id.h

@@ -73,6 +73,10 @@ class FileID {
   static std::string ConvertIdentifierToUUIDString(
       const wasteful_vector<uint8_t>& identifier);
 
+  // Convert the entire |identifier| data to a hex string.
+  static std::string ConvertIdentifierToString(
+      const wasteful_vector<uint8_t>& identifier);
+
  private:
   // Storage for the path specified
   std::string path_;