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

chrome/common/extensions/api/tab_capture_private.idl

Index: chrome/common/extensions/api/tab_capture_private.idl
diff --git a/chrome/common/extensions/api/tab_capture_private.idl b/chrome/common/extensions/api/tab_capture_private.idl
new file mode 100644
index 0000000000000000000000000000000000000000..12cd16755b37bc642e240b0d6e27e1dfe5e022b2
--- /dev/null
+++ b/chrome/common/extensions/api/tab_capture_private.idl
@@ -0,0 +1,24 @@
+// Copyright (c) 2015 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.
+
+// The <code>chrome.tabCapturePrivate</code> API provides extra functionality
+// needed by the Chrome Media Router.
+namespace tabCapturePrivate {
+  callback DoneCallback = void ();
+
+  interface Functions {
+    // Registers an off-screen tab as a "receiving browsing context" in a
+    // PresentationSession (see https://w3c.github.io/presentation-api).  The
+    // two arguments are strings identifying the off-screen tab and the
+    // PresentationSession.  The |offscreenTabId| is found as a property in the
+    // MediaStream object returned by chrome.tabCapture.captureOffscreenTab().
+    //
+    // See chrome/test/data/extensions/api_test/tab_capture/api_tests.js for
+    // usage example.
+    static void registerOffscreenTabAsPresentation(
+        DOMString offscreenTabId,
+        DOMString presentationId,
+        DoneCallback callback);
+  };
+};