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function assertViewTransitionOnNavigationImplemented() {
assert_implements(
window.CSSViewTransitionRule, "ViewTransition-on-navigation not implemented.");
}
const render_blocking_url = `resources/render-blocking-stylesheet.py`;
let render_block_uuid = null;
let render_block_reject = null;
let render_block_resolve = null;
function renderBlockingOnError() {
render_block_reject('Error while loading render blocking stylesheet.');
}
function renderBlockingOnLoad() {
render_block_resolve();
}
function blockRendering() {
if (document.body)
throw new Error('Cannot block rendering after body has been parsed.');
if (render_block_uuid)
throw new Error('Rendering already blocked.');
return new Promise((resolve, reject) => {
render_block_reject = reject;
render_block_resolve = resolve;
render_block_uuid = token();
const href = `${render_blocking_url}?key=${render_block_uuid}`;
// Need to use document.write since only parser-encountered stylesheets
// cause render blocking.
document.write(`<link rel="stylesheet" onerror="renderBlockingOnError()" onload="renderBlockingOnLoad()" href="${href}">`);
document.close();
});
}
function unblockRendering() {
if (!render_block_uuid)
throw new Error('Rendering not blocked.');
const url = `${render_blocking_url}?key=${render_block_uuid}`;
return fetch(url, { method: 'POST' }).then(response => {
if (response.status != 200) {
return response.text().then((body) => {
throw new Error('Failed to unblock rendering: ' + body);
});
}
});
}
// Use external/wpt/html/browsers/browsing-the-web/back-forward-cache/resources/executor.js
// when migrating to external WPTs.
window.disableBFCache = () => {
return new Promise(resolve => {
// Use page's UUID as a unique lock name.
navigator.locks.request("test", () => {
resolve();
return new Promise(() => {});
});
});
};
function waitForMessage(msg) {
return new Promise(resolve => {
window.addEventListener(
"message", (e) => {
if (e.data === msg)
resolve();
}
)});
}