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/pdfHandler-local.js

@@ -0,0 +1,69 @@
+/* -*- 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, isPdfDownloadable */
+
+'use strict';
+
+// The onHeadersReceived event is not generated for local resources.
+// Fortunately, local PDF files will have the .pdf extension, so there's
+// no need to detect the Content-Type
+// Unfortunately, the omnibox won't show the URL.
+// Unfortunately, this method will not work for pages in incognito mode,
+//  unless "incognito":"split" is used AND http:/crbug.com/224094 is fixed.
+
+// Keeping track of incognito tab IDs will become obsolete when
+// "incognito":"split" can be used.
+var incognitoTabIds = [];
+chrome.windows.getAll({ populate: true }, function(windows) {
+  windows.forEach(function(win) {
+    if (win.incognito) {
+      win.tabs.forEach(function(tab) {
+        incognitoTabIds.push(tab.id);
+      });
+    }
+  });
+});
+chrome.tabs.onCreated.addListener(function(tab) {
+  if (tab.incognito) incognitoTabIds.push(tab.id);
+});
+chrome.tabs.onRemoved.addListener(function(tabId) {
+  var index = incognitoTabIds.indexOf(tabId);
+  if (index !== -1) incognitoTabIds.splice(index, 1);
+});
+
+chrome.webRequest.onBeforeRequest.addListener(
+  function(details) {
+    if (isPdfDownloadable(details)) // Defined in pdfHandler.js
+      return;
+    
+    if (incognitoTabIds.indexOf(details.tabId) !== -1)
+      return; // Doesn't work in incognito mode, so don't redirect.
+
+    var viewerPage = 'content/web/viewer.html';
+    var url = chrome.extension.getURL(viewerPage) +
+      '?file=' + encodeURIComponent(details.url);
+    return { redirectUrl: url };
+  },
+  {
+    urls: [
+      'file://*/*.pdf',
+      'file://*/*.PDF'
+    ],
+    types: ['main_frame', 'sub_frame']
+  },
+  ['blocking']);