tests: Vendor blink perf tests (#38654)

Vendors the [blink perf
tests](https://chromium.googlesource.com/chromium/src/+/HEAD/third_party/blink/perf_tests/).
These perf tests are useful to evaluate the performance of servo. 
The license that governs the perf tests is included in the folder. 
Running benchmark cases automatically is left to future work.

The update.py script is taken from mozjs and slightly adapted, so we can
easily filter
(and patch if this should be necessary in the future.

Testing: This PR just adds the perf_tests, but does not use or modify
them in any way.

---------

Signed-off-by: Jonathan Schwender <schwenderjonathan@gmail.com>

tests/blink_perf_tests/get_perf_tests.sh

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+# script to vendor blink perf tests into servo.
+# At the time of writing we are mainly interested in the layout tests.
+
+set -o errexit
+set -o nounset
+set -o pipefail
+
+CHROMIUM_TAG=141.0.7354.1
+curl -LO https://chromium.googlesource.com/chromium/src/+archive/refs/tags/${CHROMIUM_TAG}/third_party/blink/perf_tests.tar.gz
+# Delete any old directory contents.
+rm -rf perf_tests && mkdir perf_tests
+tar -xf perf_tests.tar.gz -C perf_tests
+# Download license
+curl -L https://chromium.googlesource.com/chromium/src/+/refs/tags/141.0.7354.1/third_party/blink/LICENSE_FOR_ABOUT_CREDITS?format=TEXT \
+  | base64 -d > LICENSE_FOR_ABOUT_CREDITS
+git add LICENSE_FOR_ABOUT_CREDITS