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

chrome/test/automation/automation_proxy_uitest.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 <string>
 
 #include "base/command_line.h"
 #include "base/compiler_specific.h"
 #include "base/file_path.h"
 #include "base/file_util.h"
@@ skipping 45 matching lines @@
       : mock_(mock) {
     channel_id_ = AutomationProxy::GenerateChannelID();
   }
 
   AutomationProxy* CreateAutomationProxy(int execution_timeout) {
     *mock_ = new ExternalTabUITestMockClient(execution_timeout);
     (*mock_)->InitializeChannel(channel_id_, false);
     return *mock_;
   }
 
-  void InitializeConnection(const LaunchState& state,
-                            bool wait_for_initial_loads) {
-    ASSERT_TRUE(LaunchBrowserAndServer(state, wait_for_initial_loads));
+  bool InitializeConnection(
+      const LaunchState& state,
+      bool wait_for_initial_loads) OVERRIDE WARN_UNUSED_RESULT {
+    bool launch_browser_and_server =
+        LaunchBrowserAndServer(state, wait_for_initial_loads);
+    EXPECT_TRUE(launch_browser_and_server);
+    return launch_browser_and_server;
   }
 
   void TerminateConnection() {
     CloseBrowserAndServer();
   }
 
   std::string PrefixedChannelID() const {
     return channel_id_;
   }
 
@@ skipping 1577 matching lines @@
   int diff_pixels_count = 0;
   for (int x = 0; x < img_size.width(); ++x) {
     for (int y = 0; y < img_size.height(); ++y) {
       if (*snapshot_bmp.getAddr32(x, y) != *reference_bmp.getAddr32(x, y)) {
         ++diff_pixels_count;
       }
     }
   }
   ASSERT_EQ(diff_pixels_count, 0);
 }