Attach (recommended) or Link to PDF file here:
[298865.pdf](https://github.com/mozilla/pdf.js/files/2753236/298865.pdf)


Configuration:
- Web browser and its version:chrome 71.0.3578.98
- Operating system and its version:mac os 10.12.6
- PDF.js version:I use online demo in github
- Is a browser extension:no

Steps to reproduce the problem:
1. search "中华" or "电力" or so on,the highlight position is not right

What is the expected behavior? (add screenshot)
![image](https://user-images.githubusercontent.com/10000986/51087378-7eff5100-178d-11e9-991a-005d77b82f31.png)

What went wrong? (add screenshot)
![image](https://user-images.githubusercontent.com/10000986/51087374-6ee77180-178d-11e9-9707-281924f95fd0.png)

Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension):
https://mozilla.github.io/pdf.js/web/viewer.html
Util,
} from "../shared/util.js";
/**
 * Text layer render parameters.
 *
 * @typedef {Object} TextLayerRenderParameters
 * @property {import("./api").TextContent} [textContent] - Text content to
 *   render (the object is returned by the page's `getTextContent` method).
 * @property {ReadableStream} [textContentStream] - Text content stream to
 *   render (the stream is returned by the page's `streamTextContent` method).
 * @property {HTMLElement} container - HTML element that will contain text runs.
 * @property {import("./display_utils").PageViewport} viewport - The target
 *   viewport to properly layout the text runs.
 * @property {Array<HTMLElement>} [textDivs] - HTML elements that are correspond
 *   to the text items of the textContent input. This is output and shall be
 *   initially be set to empty array.
 * @property {Array<string>} [textContentItemsStr] - Strings that correspond to
 *    the `str` property of the text items of textContent input. This is output
 *   and shall be initially be set to empty array.
 * @property {number} [timeout] - Delay in milliseconds before rendering of the
 *   text runs occurs.
 * @property {boolean} [enhanceTextSelection] - Whether to turn on the text
 *   selection enhancement.
 */
const MAX_TEXT_DIVS_TO_RENDER = 100000;
const DEFAULT_FONT_SIZE = 30;
const DEFAULT_FONT_ASCENT = 0.8;
const ascentCache = new Map();
const AllWhitespaceRegexp = /^\s+$/g;
function getAscent(fontFamily, ctx) {