function assertFontSizes(msg, sizeChangesMap) {
  googObject.extend(defaultFontSizeMap, sizeChangesMap);
  for (let k in defaultFontSizeMap) {
    const node = HELPER.findTextNode(k);
    const expected = defaultFontSizeMap[k];
    if (expected) {
      assertNotNull(`${msg} [couldn't find text node "${k}"]`, node);
      assertEquals(
          `${msg} [incorrect font size for "${k}"]`, expected,
          style.getFontSize(node.parentNode));
    } else {
      assertNull(`${msg} [unexpected text node "${k}"]`, node);
    }
  }
}
Asserts that the text nodes set up by setUpFontSizeTests() have had their
font sizes changed as described by sizeChangesMap.
@param {string} msg Assertion error message.
@param {Object<string,?number>} sizeChangesMap Maps the text content of a
    text node to be measured to its expected font size in pixels, or null if
    that text node should not be present in the document (i.e. because it was
    split into two). Only the text nodes that have changed from their default
    need to be specified.