Add a fake cast extension for testing.

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 <set>
 #include <string>
@@ skipping 47 matching lines @@
 // they provide API's. If there are additional extension ids that need
 // whitelisting and are *not* the Chromecast extension, add them to a new
 // kWhitelist array.
 const char* const kChromecastExtensionIds[] = {
     "enhhojjnijigcajfphajepfemndkmdlo",  // Dev
     "pkedcjkdefgpdelpbcmbmeomcjbeemfm",  // Dogfood
     "fmfcbgogabcbclcofgocippekhfcmgfj",  // Staging
     "hfaagokkkhdbgiakmmlclaapfelnkoah",  // Canary
     "dliochdbjfkdbacpmhlcpmleaejidimm",  // Google Cast Beta
     "boadgeojelhgndaghljhdicfkmllpafd",  // Google Cast Stable
+    // Mock extension for testing, under /chrome/test/data/extensions/tray_cast
+    "hlgmmjhlnlapooncikdpiiokdjcdpjme",

[achuithb, 2015/07/08 22:23:55]

Personally I think a comment like
// Test cast extension
is sufficient, but up to you

[jdufault, 2015/07/09 19:30:02]

Done, using the string to search instead of hardcoding a path sounds much better
to me.

 };
 
 bool TabCaptureCaptureFunction::RunSync() {
   scoped_ptr<api::tab_capture::Capture::Params> params =
       TabCapture::Capture::Params::Create(*args_);
   EXTENSION_FUNCTION_VALIDATE(params.get());
 
   // Figure out the active WebContents and retrieve the needed ids.
   Browser* target_browser = chrome::FindAnyBrowser(
       GetProfile(), include_incognito(), chrome::GetActiveDesktop());
@@ skipping 101 matching lines @@
 bool TabCaptureGetCapturedTabsFunction::RunSync() {
   TabCaptureRegistry* registry = TabCaptureRegistry::Get(GetProfile());
   base::ListValue* const list = new base::ListValue();
   if (registry)
     registry->GetCapturedTabs(extension()->id(), list);
   SetResult(list);
   return true;
 }
 
 }  // namespace extensions