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

chrome/test/automation/automation_proxy_uitest.cc

Index: chrome/test/automation/automation_proxy_uitest.cc
diff --git a/chrome/test/automation/automation_proxy_uitest.cc b/chrome/test/automation/automation_proxy_uitest.cc
index 924d9879da3f2b177fb8f378b0fae0e9b8308100..665f4a2fde982daf04f7da5959a6ef8fd9ffad8d 100644
--- a/chrome/test/automation/automation_proxy_uitest.cc
+++ b/chrome/test/automation/automation_proxy_uitest.cc
@@ -63,9 +63,13 @@ class ExternalTabUITestMockLauncher : public ProxyLauncher {
     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() {