Added debugging output to mcov to help debug buildbot errors....

third_party/lcov/bin/mcov

 #!/usr/bin/perl -w
 # 
 # mcov: script to convert gcov data to lcov format on Mac.
 #
 # Based on lcov (http://ltp.sourceforge.net/coverage/lcov.php)
 # Written by ajeya at google dot com.
 #
 # usage:
 # mcov --directory <base directory> --output <output file> --verbose <level>
 #
@@ skipping 30 matching lines @@
   print " [--verbose <level>]\n";
   exit(1);
 }
 
 # convert the directory path to absolute path.
 $directory = Cwd::abs_path($directory);
 
 # convert the output file path to absolute path.
 $output_filename = Cwd::abs_path($output_filename);
 
+# Output expected args for buildbot debugging assistance.
+my $cwd = getcwd();
+print "mcov: after abs_pathing\n";
+print "mcov: getcwd() = $cwd\n";
+print "mcov: directory for data files is $directory\n";
+print "mcov: output filename is $output_filename\n";
+
+# Sanity check; die if path is wrong.
+# We don't check for output_filename because... we create it.
+if (! -d $directory) {
+  print "mcov: Bad args passed; exiting with error.\n";
+  exit(1);
+}
+
 # open file for output
 open(INFO_HANDLE, ">$output_filename");
 
 my @file_list;  # scalar to hold the list of all gcda files.
 if (-d $directory) {
   printf("Scanning $directory for $data_file_extension files ...\n");
   find(sub {
          my $file = $_;
          if ($file =~ m/\Q$data_file_extension\E$/i) {
            push(@file_list, Cwd::abs_path($file));
@@ skipping 221 matching lines @@
         push(@result, 1);
         push(@result, $number);
         push(@result, $3);
         push(@result, $2);
       }  
     }
   }
   close(INPUT);
   return @result;
 }