Update tabCapture API docs with browser action info.

chrome/common/extensions/api/tab_capture.idl

 // 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.
 
 // An API for tab media streams.
 
 namespace tabCapture {
 
   enum TabCaptureState {
     pending,
@@ skipping 29 matching lines @@
     MediaStreamConstraint? videoConstraints;
   };
 
   callback GetTabMediaCallback =
       void ([instanceOf=LocalMediaStream] object stream);
 
   callback GetCapturedTabsCallback = void (CaptureInfo[] result);
 
   interface Functions {
     // Captures the visible area of the currently active tab.
-    // Extensions must have the "tabCapture" permission to use this method.
+    // This method can only be used on the currently active page after the
+    // extension has been <em>invoked</em>, similar to the way that
+    // <a href="activeTab.html">activeTab</a> works.
+    // Note that Chrome internal pages cannot be captured.
     // |options| : Configures the returned media stream.
     // |callback| : Callback with either the stream returned or null.
     static void capture(CaptureOptions options,
                         GetTabMediaCallback callback);
 
     // Returns a list of tabs that have requested capture or are being
     // captured, i.e. status != stopped and status != error.
     // This allows extensions to inform the user that there is an existing
     // tab capture that would prevent a new tab capture from succeeding (or
     // to prevent redundant requests for the same tab).
     static void getCapturedTabs(GetCapturedTabsCallback callback);
   };
 
   interface Events {
     // Event fired when the capture status of a tab changes.
     // This allows extension authors to keep track of the capture status of
     // tabs to keep UI elements like page actions and infobars in sync.
     static void onStatusChanged(CaptureInfo info);
   };
 
 };