New tabCapture.captureOffscreenTab API, initially for Presentation API 1UA mode

chrome/renderer/resources/extensions/tab_capture_custom_bindings.js

Index: chrome/renderer/resources/extensions/tab_capture_custom_bindings.js
diff --git a/chrome/renderer/resources/extensions/tab_capture_custom_bindings.js b/chrome/renderer/resources/extensions/tab_capture_custom_bindings.js
index 93a60549e3743d366c47fabe14f7d8c63bff316d..ab16dfb60e3c0d877df04128050e8a1d77326366 100644
--- a/chrome/renderer/resources/extensions/tab_capture_custom_bindings.js
+++ b/chrome/renderer/resources/extensions/tab_capture_custom_bindings.js
@@ -9,8 +9,7 @@ var binding = require('binding').Binding.create('tabCapture');
 binding.registerCustomHook(function(bindingsAPI, extensionId) {
   var apiFunctions = bindingsAPI.apiFunctions;
 
-  apiFunctions.setCustomCallback('capture',
-      function(name, request, callback, response) {
+  function proxyToGetUserMedia(name, request, callback, response) {
     if (!callback)
       return;
 
@@ -24,14 +23,17 @@ binding.registerCustomHook(function(bindingsAPI, extensionId) {
       try {
         navigator.webkitGetUserMedia(options,
                                      function(stream) { callback(stream); },
-                                     function() { callback(null); });
+                                     function(exception) { callback(null); });
       } catch (e) {
         callback(null);
       }
     } else {
       callback(null);
     }
-  });
+  }
+
+  apiFunctions.setCustomCallback('capture', proxyToGetUserMedia);
+  apiFunctions.setCustomCallback('capturePresentation', proxyToGetUserMedia);
 });
 
 exports.binding = binding.generate();