<!DOCTYPE html>
<style>
    #test {
        width: 200px;
        border: 2px solid black;
        height: 40px;
        resize: none;
        overflow: hidden;
    }
</style>
<textarea id="test">Some text</textarea>
<script>
  window.onload = function() {
    if (window.testRunner) {
      testRunner.waitUntilDone();
      document.getElementById("test").focus();
      testRunner.setBackingScaleFactor(0.9,
        function() {
          if (window.testRunner)
            testRunner.notifyDone();
        }
      );
    }
  }
</script>