Update tabCapture API docs with browser action info.

chrome/browser/extensions/api/tab_capture/tab_capture_api.cc

 // 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.
 
 // Implements the Chrome Extensions Tab Capture API.
 
 #include "chrome/browser/extensions/api/tab_capture/tab_capture_api.h"
 
 #include "base/command_line.h"
 #include "base/stringprintf.h"
@@ skipping 23 matching lines @@
 
 namespace extensions {
 
 namespace {
 
 const char kCapturingSameTab[] = "Cannot capture a tab with an active stream.";
 const char kFindingTabError[] = "Error finding tab to capture.";
 const char kNoAudioOrVideo[] = "Capture failed. No audio or video requested.";
 const char kPermissionError[] = "Tab Capture API flag is not enabled.";
 const char kGrantError[] =
-    "Capture of this tab must be granted by clicking on the extension icon.";
+    "Extension has not been invoked for the current page (see activeTab "
+    "permission). Chrome pages cannot be captured.";
 
 // Keys/values for media stream constraints.
 const char kMediaStreamSource[] = "chromeMediaSource";
 const char kMediaStreamSourceId[] = "chromeMediaSourceId";
 const char kMediaStreamSourceTab[] = "tab";
 
 }  // namespace
 
 bool TabCaptureCaptureFunction::RunImpl() {
   if (!FeatureSwitch::tab_capture()->IsEnabled()) {
@@ skipping 118 matching lines @@
     info->tab_id = it->first;
     info->status = it->second;
     list->Append(info->ToValue().release());
   }
 
   SetResult(list);
   return true;
 }
 
 }  // namespace extensions