Implement Chrome Extension TabCapture API.

chrome/renderer/resources/extensions/experimental.tab_capture_custom_bindings.js

+// Copyright (c) 2012 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.
+
+// Custom bindings for the Tab Capture API.
+
+var tabCaptureNatives = requireNative('experimental_tabCapture');
+var chromeHidden = requireNative('chrome_hidden').GetChromeHidden();
+
+chromeHidden.registerCustomHook('experimental.tabCapture',
+                                function(bindingsAPI, extensionId) {
+  var apiFunctions = bindingsAPI.apiFunctions;
+
+  apiFunctions.setCustomCallback('getTabMedia',
+                                 function(name, request, response) {
+    if (response && request.callback) {
+      var callback = request.callback;
+      var successFunc = function(stream) {
+        callback(stream);
+      };
+      var errorFunc = function() {
+        callback(null);
+      };
+      var videoConstraints = false;
+      var audioConstraints = false;
+
+      // TODO(justinlin): Merge with other constraints when they land.
+      if (response.options.video) {
+        videoConstraints = {
+          mandatory: {
+            chromeMediaSource: 'tab',
+            chromeMediaSourceId: response.deviceId
+          }
+        };
+      }
+
+      if (response.options.audio) {
+        audioConstraints = {
+          mandatory: {
+            chromeMediaSource: 'tab',
+            chromeMediaSourceId: response.deviceId
+          }
+        };
+      }
+
+      var options = {};
+      options.video = videoConstraints;
+      options.audio = audioConstraints;
+
+      navigator.webkitGetUserMedia(options, successFunc, errorFunc);

[Aaron Boodman, 2012/10/04 07:21:43]

What prevents bad extensions from just calling this with whatever tabId they
want? Is permission checked somewhere behind this webkit call?

[justinlin, 2012/10/08 09:58:31]

Do you mean what prevents any normal page calling this method? I added a check
so that the mediaSource constraints are only respected if called from a chrome
extension, so normal pages can't use tabCapture, only extensions can. However,
the purpose of this API is to be able to capture any tab, so you should be able
to specify any tabId you want for the extension API.

+    }
+    request.callback = null;
+  });
+});