Enable experimental support for sub-pixel font scaling

LayoutTests/fast/text/sub-pixel/resources/text-scaling.js

+var TOLERANCE = 0.01;
+
+var FONT_SIZE_START = 10;
+var FONT_SIZE_BASELINE = 12;
+var FONT_SIZE_STEP = 0.25;
+var FONT_SIZE_END = 25;
+
+var PASS = 0;
+var FAIL = 1;
+
+function numberToNode(n)
+{
+    return document.createTextNode(n.toFixed(2));
+}
+
+function createElement(type, opt_textContent, opt_className)
+{
+    var el = document.createElement(type);
+    if (opt_className)
+        el.className = opt_className;
+    if (opt_textContent)
+        el.appendChild(document.createTextNode(opt_textContent));
+    return el;
+}
+
+function runTest(containerEl, pangram, opt_writingMode)
+{
+    var cont = document.getElementById('test');
+
+    var el = createElement('div', undefined, 'header');
+    el.appendChild(createElement('div', 'Font Size'));
+    el.appendChild(createElement('div', 'Width'));
+    el.appendChild(createElement('div', 'Normalized'));
+    el.appendChild(createElement('div', 'Diff'));
+    el.appendChild(createElement('span', 'Content'));
+    containerEl.appendChild(el);
+
+    var referenceElement;
+    for (var fontSize = FONT_SIZE_START;
+            fontSize < FONT_SIZE_END;
+            fontSize += FONT_SIZE_STEP) {
+        var el = createElement('div');
+        el.appendChild(createElement('div'));
+        el.appendChild(createElement('div'));
+        el.appendChild(createElement('div'));
+        el.appendChild(createElement('div', undefined, 'results'));
+        var textSpan = createElement('span');
+        el.appendChild(textSpan);
+        textSpan.appendChild(document.createTextNode(pangram));
+        textSpan.style.fontSize = fontSize;
+        containerEl.appendChild(el);
+        if (fontSize == FONT_SIZE_BASELINE)
+            referenceElement = el;
+    }
+
+    referenceElement.className = 'reference';
+    var rect = referenceElement.lastChild.getBoundingClientRect();
+    var expectedWidth = opt_writingMode == 'vertical' ? rect.height : rect.width;
+
+    var failures = 0;
+    for (var row, i = 0; row = containerEl.children[i + 1]; i++) {
+        var rect = row.lastChild.getBoundingClientRect();
+        var fontSize = FONT_SIZE_START + (FONT_SIZE_STEP * i);
+        var width = opt_writingMode == 'vertical' ? rect.height : rect.width;
+        var normalizedWidth = (width / fontSize) * FONT_SIZE_BASELINE;
+        row.children[0].appendChild(numberToNode(fontSize));
+        row.children[1].appendChild(numberToNode(width));
+        row.children[2].appendChild(numberToNode(normalizedWidth));
+        row.children[3].appendChild(numberToNode(normalizedWidth - expectedWidth));
+        if (Math.abs(expectedWidth - normalizedWidth) <= TOLERANCE) {
+            row.classList.add('size-pass');
+        } else {
+            row.classList.add('size-fail');
+            failures++
+        }
+    }
+
+    return failures ? FAIL : PASS;
+}