Add a mimeHandler extension API.

chrome/browser/resources/pdf/main.js

 // Copyright 2014 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.
 
 'use strict';
 
 /**
  * Global PDFViewer object, accessible for testing.
  * @type Object
  */
@@ skipping 22 matching lines @@
    *     contained in the PDF.
    */
   function initViewer(streamDetails) {
     // PDFViewer will handle any messages after it is created.
     window.removeEventListener('message', handleScriptingMessage, false);
     viewer = new PDFViewer(streamDetails);
     while (pendingMessages.length > 0)
       viewer.handleScriptingMessage(pendingMessages.shift());
   }
 
+  function generateStreamDetailsAndInitViewer() {
+    var url = window.location.search.substring(1);
+    var streamDetails = {
+      streamUrl: url,
+      originalUrl: url,
+      responseHeaders: '',
+      embedded: window.parent != window,
+      tabId: -1
+    };
+    if (chrome.tabs) {
+      chrome.tabs.getCurrent(function(tab) {
+        streamDetails.tabId = tab.id;
+        initViewer(streamDetails);
+      });
+      return;
+    }
+    initViewer(streamDetails);

[raymes, 2015/01/12 05:26:04]

See my comment below about putting the synchronous case first with the early
return. WDYT?

[Sam McNally, 2015/01/12 07:13:35]

Done.

+  }
+
   /**
    * Entrypoint for starting the PDF viewer. This function obtains the details
    * of the PDF 'stream' (the data that points to the PDF) and constructs a
    * PDFViewer object with it.
    */
   function main() {
     // Set up an event listener to catch scripting messages which are sent prior
     // to the PDFViewer being created.
     window.addEventListener('message', handleScriptingMessage, false);
 
-    // If the viewer is started from the browser plugin, the view ID will be
-    // passed in which identifies the instance of the plugin.
-    var params = window.location.search.substring(1).split('=');
-    if (params.length == 2 && params[0] == 'id') {
-      var viewId = params[1];
-
-      // Send a message to the background page to obtain the stream details. It
-      // will run the callback function passed in to initialize the viewer.
-      chrome.runtime.sendMessage(
-          'mhjfbmdgcfjbbpaeojofohoefgiehjai',
-          {viewId: viewId},
-          initViewer);
+    // If the viewer is started from the browser plugin, getStreamInfo will
+    // return the details of the stream.
+    if (chrome.mimeHandler) {
+      chrome.mimeHandler.getStreamInfo(function(streamDetails) {
+        if (streamDetails) {
+          initViewer(streamDetails);
+          return;
+        }
+        generateStreamDetailsAndInitViewer();

[raymes, 2015/01/12 05:26:04]

I think an if/else here might be cleaer

[Sam McNally, 2015/01/12 07:13:35]

Done.

+      });
       return;
     }
-
-    // The viewer may be started directly by passing in the URL of the PDF to
-    // load as the query string. This is used for print preview in particular.
-    // The URL of this page will be of the form
-    // 'chrome-extension://<extension id>?<pdf url>'. We pull out the <pdf url>
-    // part here.
-    var url = window.location.search.substring(1);
-    var streamDetails = {
-      streamUrl: url,
-      originalUrl: url,
-      responseHeaders: '',
-      embedded: window.parent != window,
-      tabId: -1
-    };
-    if (!chrome.tabs) {
-      initViewer(streamDetails);
-      return;
-    }
-    chrome.tabs.getCurrent(function(tab) {
-      if (tab && tab.id != undefined)
-        streamDetails.tabId = tab.id;
-      initViewer(streamDetails);
-    });
-  }
+    generateStreamDetailsAndInitViewer();

[raymes, 2015/01/12 05:26:04]

Could you put the synchronous case first? This might be clearer, e.g. 

if (!chrome.mimHandler) {
  generateStreamDetailsAndInitViewer();
  return;
}

...

[Sam McNally, 2015/01/12 07:13:35]

Done.

+  };
 
   main();
 })();