Remove <pre></pre> from empty summary.

This causes blank test_logs (which may come when a test crashes)
to just be <pre></pre> causing the summary to think there is
content.

Bug: 1151186
Change-Id: Ie31dcaa4d7ed0d7318eb2e2485b71147f00fc36c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2566694Reviewed-by: Peter Wen <wnwen@chromium.org>
Reviewed-by: Nodir Turakulov <nodir@chromium.org>
Commit-Queue: benjamin joyce <bjoyce@chromium.org>
Cr-Commit-Position: refs/heads/master@{#832478}

build/android/OWNERS

+bjoyce@chromium.org
 jbudorick@chromium.org
 mheikal@chromium.org
 pasko@chromium.org

build/android/pylib/base/result_sink.py

@@ -84,7 +84,7 @@ class ResultSinkClient(object):
     if len(test_log) > report_check_size:
       test_log_formatted = ('<pre>' + test_log[:report_check_size] +
                             '...Full output in Artifact.</pre>')
-    else:
+    elif test_log:
       test_log_formatted = '<pre>' + test_log + '</pre>'
 
     tr = {