Let pyauto create an attached webdriver instance to manipulate web pages.

chrome/test/ui/ui_test.cc

 // Copyright (c) 2011 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.
 
 #include "chrome/test/ui/ui_test.h"
 
 #if defined(OS_POSIX)
 #include <signal.h>
 #include <sys/types.h>
 #endif
@@ skipping 107 matching lines @@
   if (!launcher_.get())
     launcher_.reset(CreateProxyLauncher());
   launcher_->AssertAppNotRunning("Please close any other instances "
                                  "of the app before testing.");
 
   JavaScriptExecutionController::set_timeout(
       TestTimeouts::action_max_timeout_ms());
   test_start_time_ = Time::NowFromSystemTime();
 
   SetLaunchSwitches();
-  launcher_->InitializeConnection(DefaultLaunchState(),
-                                  wait_for_initial_loads_);
+  ASSERT_TRUE(launcher_->InitializeConnection(DefaultLaunchState(),
+                                              wait_for_initial_loads_));
 }
 
 void UITestBase::TearDown() {
   if (launcher_.get())
     launcher_->TerminateConnection();
 
   // Make sure that we didn't encounter any assertion failures
   logging::AssertionList assertions;
   logging::GetFatalAssertions(&assertions);
 
@@ skipping 641 matching lines @@
     base::PlatformThread::Sleep(TestTimeouts::action_timeout_ms() / kCycles);
   }
 
   LOG(INFO) << "Elapsed time: " << (base::Time::Now() - start).InSecondsF()
             << " seconds"
             << " call failed " << fail_count << " times"
             << " state was incorrect " << incorrect_state_count << " times";
   ADD_FAILURE() << "Timeout reached in " << __FUNCTION__;
   return false;
 }