ui/file_manager/file_manager/foreground/elements/files_safe_media_webview_content.js

// Copyright 2016 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

window.onload = function() {
  var FILES_APP_ORIGIN = 'chrome-extension://hhaomjibdihmijegdhdafkllkbggdgoj';
  var messageSource;

  var content = document.querySelector('#content');

  window.addEventListener('message', function(event) {
    if (event.origin !== FILES_APP_ORIGIN) {
      console.error('Unknown origin: ' + event.origin);
      return;
    }

    messageSource = event.source;
    switch (event.data.type) {
      case 'html':
        content.textContent = '';
        contentChanged(null);
        fetch(event.data.src).then((response) => {
          return response.text();
        }).then((text) => {
          content.textContent = text;
          contentChanged(text);
        });
        break;
      default:
        content.src = event.data.src;
        contentChanged(content.src);
        break;
    }
  });

  document.addEventListener('contextmenu', function(e) {
    e.preventDefault();
    return false;
  });

  document.addEventListener('click', function(e) {
    sendMessage((e.target === content) ? 'tap-inside' : 'tap-outside');
  });

  function contentChanged(src) {
    sendMessage(src ? 'webview-loaded' : 'webview-cleared');
  }

  function sendMessage(message) {
    if (messageSource) {
      messageSource.postMessage(message, FILES_APP_ORIGIN);
    }
  }

  // TODO(oka): This is a workaround to fix FOUC problem, where sometimes
  // immature view with smaller window size than outer window is rendered for a
  // moment. Remove this after the root cause is fixed. http://crbug.com/640525
  window.addEventListener('resize', function() {
    // Remove hidden attribute on event of resize to avoid FOUC. The window's
    // initial size is 100 x 100 and it's fit into the outer window size after a
    // moment. Due to Files App's window size constraint, resized window must be
    // larger than 100 x 100. So this event is always invoked.
    content.removeAttribute('hidden');
  });
  // Fallback for the case of webview bug is fixed and above code is not
  // executed.
  setTimeout(function() {
    content.removeAttribute('hidden');
  }, 500);
};