[piexwasm] Add tests.sh script

Running tests will require a http server, puppeteer and some .js files
to do the actual testing in a browser. Add a script to drive the whole
testing process. Output:

  % npm run test
  tests PASS

If there was a test failure, a test.log is available to figure out the
problem.

Bug: 935285
Change-Id: I12f69008d37c67433901ed6a37a3d7e9375abac3
Reviewed-on: https://chromium-review.googlesource.com/c/1491155Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#635923}

ui/file_manager/image_loader/piex/tests.sh

+#!/bin/bash
+
+# Copyright 2019 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+PORT=8123
+HTTP="http://localhost:${PORT}"
+
+# Start test http server.
+echo -e "test: starting test server ${HTTP}\n" > tests.log
+node node_modules/http-server/bin/http-server -p ${PORT} > /dev/null 2>&1 &
+HTTP_SERVER_PID=$!
+
+# Extract preview thumbnails from the raw test images.
+rm -f tests.hash
+node tests.js ${HTTP}/tests.html "$*" | tee -a tests.log | \
+  grep hash > tests.hash
+kill ${HTTP_SERVER_PID} > /dev/null 2>&1
+
+# Compare their hash to the golden hash values.
+if [[ $(cmp tests.hash images.golden.hash) ]]; then
+  echo "tests FAIL" || exit 1
+else
+  echo "tests PASS"
+fi