Always write index.html

tools/run_tests/run_microbenchmark.py

@@ -228,10 +228,11 @@ argp.add_argument('--summary_time',
                   help='Minimum time to run benchmarks for the summary collection')
 args = argp.parse_args()
 
-for bm_name in args.benchmarks:
+try:
+  for bm_name in args.benchmarks:
     for collect in args.collect:
       collectors[collect](bm_name, args)
-if args.diff_perf:
+  if args.diff_perf:
     if 'summary' not in args.collect:
       for bm_name in args.benchmarks:
         run_summary(bm_name, 'opt', bm_name)
@@ -259,7 +260,7 @@ if args.diff_perf:
       if diff:
         heading('Performance diff: %s' % bm_name)
         text(diff)
-
-index_html += "</body>\n</html>\n"
-with open('reports/index.html', 'w') as f:
+finally:
+  index_html += "</body>\n</html>\n"
+  with open('reports/index.html', 'w') as f:
     f.write(index_html)