tor-browser

The Tor Browser
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web-font-styled-text-resize-swap.html (2209B)

      1 <!doctype html>
      2 <script src="/resources/testharness.js"></script>
      3 <script src="/resources/testharnessreport.js"></script>
      4 <style>
      5  @font-face {
      6    font-family: "ADTestFaceSwap";
      7    src: url("/fonts/AD.woff?pipe=trickle(d0.5)");
      8    font-display: swap;
      9  }
     10 
     11  .test {
     12    font-family: "ADTestFaceSwap";
     13  }
     14 </style>
     15 <!--
     16  Web-font styled text that gets resized during swap period should make a
     17  LCP emission if the new size is larger than the existing LCP element size.
     18 -->
     19 <div class="test">LCP: Web Font Styled Text Resize</div>
     20 <script>
     21  promise_test(async (t) => {
     22    await document.fonts.ready;
     23 
     24    // Verify web font is downloaded.
     25    assert_own_property(window, "PerformanceResourceTiming", "ResourceTiming not supported");
     26    let url = "/fonts/AD.woff?pipe=trickle(d0.5)";
     27    var absoluteURL = new URL(url, location.href).href;
     28    assert_equals(
     29      performance.getEntriesByName(absoluteURL).length,
     30      1,
     31      "Web font should be downloaded",
     32    );
     33 
     34    // Verify web font is available.
     35    assert_true(document.fonts.check("16px ADTestFaceSwap"), "Font should be the web font added");
     36 
     37    let lcpEntries = [];
     38    await Promise.race([
     39      new Promise((resolve, reject) => {
     40        t.step_timeout(() => {
     41          resolve(lcpEntries);
     42        }, 3000);
     43      }),
     44      new Promise((resolve, reject) => {
     45        new PerformanceObserver((list, observer) => {
     46          lcpEntries.push(...list.getEntries());
     47          if (lcpEntries.length >= 2) {
     48            resolve();
     49            observer.disconnect();
     50          }
     51        }).observe({ type: "largest-contentful-paint", buffered: true });
     52      }),
     53    ]);
     54 
     55    // Verify there are 2 LCP entries emitted.
     56    assert_equals(
     57      lcpEntries.length,
     58      2,
     59      "There should be 2 LCP entries. The 1st one corresponds to the system font and the 2nd the web font.",
     60    );
     61 
     62    // Verify the size of 2nd LCP entry is larger than that of the 1st one.
     63    assert_greater_than(
     64      lcpEntries[1].size,
     65      lcpEntries[0].size,
     66      "The size of 2ndLCP entry should be larger than that of the 1st one.",
     67    );
     68  }, "LCP should be updated if the web font styled text resizes to be larger during the swap period");
     69 </script>