Add performance tests for long words/lines

third_party/WebKit/PerformanceTests/Layout/resources/line-layout-perf-test.js

+'use strict';
+
+class LineLayoutPerfTest {
+  constructor(container) {
+    this.container = container;
+    this.spanCount = 1;
+    this.lineCount = 10000;
+    this.wordCountPerLine = 20;
+    this.uniqueWordCount = 100;
+    this.wordLength = 8;
+    this.wordSeparator = ' ';
+  }
+
+  run(description) {
+    // Unblock onload event by scheduling with zero delay,
+    // in order to avoid perf bot flakiness where the bot checks
+    // for timeouts reaching onload event, see crbug.com/457194
+    window.setTimeout(() => {
+      PerfTestRunner.measureTime({
+        description: description,
+        run: this.measure.bind(this)
+      });
+    }, 0);
+  }
+
+  measure() {
+    var fragment = this.createFragment();
+    PerfTestRunner.forceLayout();
+
+    var now = PerfTestRunner.now();
+    this.container.appendChild(fragment);
+    PerfTestRunner.forceLayout();
+    var resultTime = PerfTestRunner.now() - now;
+
+    while (this.container.firstChild)
+      this.container.removeChild(this.container.firstChild);

[eae, 2016/08/29 16:32:57]

It's faster the remove the lastChild (but keep checking for firstChild in the
loop condition). 

[kojii, 2016/08/29 19:14:51]

Didn't know that, thank you!

+    return resultTime;
+  }
+
+  createFragment() {
+    return TextGenerator.createFragment(this.spanCount, this.lineCount,
+      this.wordCountPerLine, this.wordSeparator,
+      this.createWordGenerator());
+  }
+
+  createWordGenerator() {
+    return TextGenerator.createWordPoolGenerator(this.uniqueWordCount, this.wordLength);
+  }
+}
+
+class LongWordPerfTest extends LineLayoutPerfTest {
+  constructor(container, wordLength) {
+    super(container);
+    this.lineCount = 1;
+    this.wordCountPerLine = 1;
+    this.wordLength = wordLength;
+  }
+
+  createWordGenerator() {
+    return () => TextGenerator.createWord(this.wordLength);
+  }
+}
+
+class TextGenerator {
+  static createFragment(spanCount, lineCount, wordCountPerLine, wordSeparator, nextWord) {
+    if (spanCount <= 0)
+      return document.createTextNode(TextGenerator.createLines(lineCount, wordCountPerLine, wordSeparator, nextWord));
+
+    var fragment = document.createDocumentFragment();

[eae, 2016/08/29 16:32:57]

Any particular reason you're using a document fragment instead of a container
element? Just curious.

[kojii, 2016/08/29 19:14:50]

In order not to create additional span to wrap, while single appendChild to add
multiple spans. Probably additional span does not matter though.

+    for (var elementIndex = 0; elementIndex < spanCount; elementIndex++) {
+      var child = document.createElement('span');
+      child.textContent = TextGenerator.createLines(lineCount, wordCountPerLine, wordSeparator, nextWord);
+      fragment.appendChild(child);
+    }
+    return fragment;
+  }
+
+  static createLines(lineCount, wordCountPerLine, wordSeparator, nextWord) {
+    var lines = [];
+    for (var lineIndex = 0; lineIndex < lineCount; lineIndex++)
+      lines.push(this.createLine(wordCountPerLine, wordSeparator, nextWord));
+    return lines.join('\n');
+  }
+
+  static createLine(wordCountPerLine, wordSeparator, nextWord) {
+    let words = [];
+    for (var wordIndex = 0; wordIndex < wordCountPerLine; wordIndex++)
+      words.push(nextWord());
+    return words.join(wordSeparator);
+  }
+
+  static createWordPoolGenerator(wordCount, wordLength) {
+    var words = [];
+    for (var i = 0; i < wordCount; i++)
+      words.push(TextGenerator.createWord(wordLength));
+    return () => {
+      return words[Math.floor(Math.random() * words.length)];
+    };
+  }
+
+  static createWord(length) {
+    var pieces = [];
+    while (length > 0) {
+      var piece = Math.random().toString(36).slice(2);
+      pieces.push(piece.slice(0, length));
+      length -= piece.length;
+    }
+    return pieces.join('');
+  }
+}