Fix url building for printer attribute queries.

We're building urls to make printer attribute requests to printers
directly to check for autoconf support and connectivity.  Ensure that
there is only one '/' between the authority and queue.

Bug: 819280
Change-Id: I0be201f46b344b807e121326f9bbf1d86565de32
Reviewed-on: https://chromium-review.googlesource.com/960939
Commit-Queue: Sean Kau <skau@chromium.org>
Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543465}

printing/backend/cups_jobs.cc

@@ -450,9 +450,15 @@ bool GetPrinterInfo(const std::string& address,
     return false;
   }
 
+  // TODO(crbug.com/821497): Use a library to canonicalize the URL.
+  size_t first_non_slash = resource.find_first_not_of('/');
+  const std::string path = (first_non_slash == std::string::npos)
+                               ? ""
+                               : resource.substr(first_non_slash);
+
   std::string printer_uri =
       base::StringPrintf("%s://%s:%d/%s", encrypted ? kIppsScheme : kIppScheme,
-                         address.c_str(), port, resource.c_str());
+                         address.c_str(), port, path.c_str());
 
   ipp_status_t status;
   ScopedIppPtr response =