LibWeb: Add some compression WPT tests

These are relevant for the next commits.

Tests/LibWeb/Text/input/wpt-import/compression/compression-multiple-chunks.tentative.any.js

@@ -0,0 +1,67 @@
+// META: global=window,worker,shadowrealm
+// META: script=third_party/pako/pako_inflate.min.js
+// META: timeout=long
+
+'use strict';
+
+// This test asserts that compressing multiple chunks should work.
+
+// Example: ('Hello', 3) => TextEncoder().encode('HelloHelloHello')
+function makeExpectedChunk(input, numberOfChunks) {
+  const expectedChunk = input.repeat(numberOfChunks);
+  return new TextEncoder().encode(expectedChunk);
+}
+
+// Example: ('Hello', 3, 'deflate') => compress ['Hello', 'Hello', Hello']
+async function compressMultipleChunks(input, numberOfChunks, format) {
+  const cs = new CompressionStream(format);
+  const writer = cs.writable.getWriter();
+  const chunk = new TextEncoder().encode(input);
+  for (let i = 0; i < numberOfChunks; ++i) {
+    writer.write(chunk);
+  }
+  const closePromise = writer.close();
+  const out = [];
+  const reader = cs.readable.getReader();
+  let totalSize = 0;
+  while (true) {
+    const { value, done } = await reader.read();
+    if (done)
+      break;
+    out.push(value);
+    totalSize += value.byteLength;
+  }
+  await closePromise;
+  const concatenated = new Uint8Array(totalSize);
+  let offset = 0;
+  for (const array of out) {
+    concatenated.set(array, offset);
+    offset += array.byteLength;
+  }
+  return concatenated;
+}
+
+const hello = 'Hello';
+
+for (let numberOfChunks = 2; numberOfChunks <= 16; ++numberOfChunks) {
+  promise_test(async t => {
+    const compressedData = await compressMultipleChunks(hello, numberOfChunks, 'deflate');
+    const expectedValue = makeExpectedChunk(hello, numberOfChunks);
+    // decompress with pako, and check that we got the same result as our original string
+    assert_array_equals(expectedValue, pako.inflate(compressedData), 'value should match');
+  }, `compressing ${numberOfChunks} chunks with deflate should work`);
+
+  promise_test(async t => {
+    const compressedData = await compressMultipleChunks(hello, numberOfChunks, 'gzip');
+    const expectedValue = makeExpectedChunk(hello, numberOfChunks);
+    // decompress with pako, and check that we got the same result as our original string
+    assert_array_equals(expectedValue, pako.inflate(compressedData), 'value should match');
+  }, `compressing ${numberOfChunks} chunks with gzip should work`);
+
+  promise_test(async t => {
+    const compressedData = await compressMultipleChunks(hello, numberOfChunks, 'deflate-raw');
+    const expectedValue = makeExpectedChunk(hello, numberOfChunks);
+    // decompress with pako, and check that we got the same result as our original string
+    assert_array_equals(expectedValue, pako.inflateRaw(compressedData), 'value should match');
+  }, `compressing ${numberOfChunks} chunks with deflate-raw should work`);
+}