Highly improved Chrome extension

Full list feature changes in this commit:
- Support for iframes
- Switched to content-type (MIME) detection instead of hard-coding a
  case-sensitive check for the .PDF extension
- The PDF's original URL is visible in the omnibox
- Support for incognito mode

Note: PDF viewer is disabled for the file:// + incognito
combination, because it's currently impossible to get the combination
to work.

See https://github.com/mozilla/pdf.js/pull/3017#issuecomment-15693432

extensions/chrome/insertviewer.js

@@ -0,0 +1,128 @@
+/* -*- Mode: Java; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set shiftwidth=2 tabstop=2 autoindent cindent expandtab: */
+/*
+Copyright 2012 Mozilla Foundation
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+/* globals chrome */
+
+'use strict';
+
+var VIEWER_URL = chrome.extension.getURL('content/web/viewer.html');
+var BASE_URL = VIEWER_URL.replace(/[^\/]+$/, '');
+
+function getViewerURL(pdf_url) {
+  return VIEWER_URL + '?file=' + encodeURIComponent(pdf_url);
+}
+
+function showViewer(url) {
+  // Cancel page load and empty document.
+  window.stop();
+  document.body.textContent = '';
+  
+  replaceDocumentWithViewer(url);
+}
+function makeLinksAbsolute(doc) {
+  normalize('href', 'link[href]');
+  normalize('src', 'style[src],script[src]');
+
+  function normalize(attribute, selector) {
+    var nodes = doc.querySelectorAll(selector);
+    for (var i=0; i<nodes.length; ++i) {
+      var node = nodes[i];
+      var newAttribute = makeAbsolute(node.getAttribute(attribute));
+      node.setAttribute(attribute, newAttribute);
+    }
+  }
+  function makeAbsolute(url) {
+    if (url.indexOf('://') !== -1) return url;
+    return BASE_URL + url;
+  }
+}
+function replaceDocumentWithViewer(url) {
+  var x = new XMLHttpRequest();
+  x.open('GET', VIEWER_URL);
+  x.responseType = 'document';
+  x.onload = function() {
+    // Resolve all relative URLs
+    makeLinksAbsolute(x.response);
+
+    // Remove all <script> elements (added back later).
+    // I assumed that no inline script tags exist.
+    var scripts = [];
+    while (x.response.scripts.length) {
+      var script = x.response.scripts[0];
+      var newScript = document.createElement('script');
+      newScript.onload = loadNextScript;
+      newScript.src = script.src;
+      script.parentNode.removeChild(script);
+      scripts.push(newScript);
+    }
+
+    // Replace document with viewer
+    var docEl = document.adoptNode(x.response.documentElement);
+    document.replaceChild(docEl, document.documentElement);
+    // Force Chrome to render content
+    // (without this line, the layout is broken and querySelector
+    //  fails to find elements, even when they appear in the doc)
+    document.body.innerHTML += '';
+
+    // Load all scripts
+    loadNextScript();
+
+    function loadNextScript() {
+      if (scripts.length > 0)
+        document.head.appendChild(scripts.shift());
+      else
+        renderPDF(url);
+    }
+  };
+  x.send();
+}
+function renderPDF(url) {
+  var args = {
+    BASE_URL: BASE_URL,
+    pdf_url: url
+  };
+  // The following technique is explained at
+  // http://stackoverflow.com/a/9517879/938089
+  var script = document.createElement('script');
+  script.textContent =
+  '(function(args) {' +
+  '  PDFJS.workerSrc = args.BASE_URL + PDFJS.workerSrc;' +
+  '  window.DEFAULT_URL = args.pdf_url;' +
+  '  window.IMAGE_DIR = args.BASE_URL + window.IMAGE_DIR;' +
+  '})(' + JSON.stringify(args) + ');';
+  document.head.appendChild(script);
+
+  // Trigger domready
+  if (document.readyState === 'complete') {
+    var event = document.createEvent('Event');
+    event.initEvent('DOMContentLoaded', true, true);
+    document.dispatchEvent(event);
+  }
+}
+
+
+// Activate the content script only once per frame (until reload)
+if (!window.hasRun) {
+  window.hasRun = true;
+  chrome.extension.onMessage.addListener(function listener(message) {
+    if (message && message.type === 'showPDFViewer' &&
+        message.url === location.href) {
+          chrome.extension.onMessage.removeListener(listener);
+          showViewer(message.url);
+        }
+  });
+}