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

chrome/test/automation/proxy_launcher.cc

Index: chrome/test/automation/proxy_launcher.cc
diff --git a/chrome/test/automation/proxy_launcher.cc b/chrome/test/automation/proxy_launcher.cc
index 69742aa178fdee05d3730f0ab5cc8c7a2ef67b3c..c7aa01ff48930de3d9fed908d076ed1f35427c54 100644
--- a/chrome/test/automation/proxy_launcher.cc
+++ b/chrome/test/automation/proxy_launcher.cc
@@ -505,9 +505,11 @@ base::TimeDelta ProxyLauncher::browser_quit_time() const {
 
 NamedProxyLauncher::NamedProxyLauncher(const std::string& channel_id,
                                        bool launch_browser,
+                                       bool wait_for_server_channel,
                                        bool disconnect_on_failure)
     : channel_id_(channel_id),
       launch_browser_(launch_browser),
+      wait_for_server_channel_(wait_for_server_channel),
       disconnect_on_failure_(disconnect_on_failure) {
 }
 
@@ -542,19 +544,21 @@ bool NamedProxyLauncher::InitializeConnection(const LaunchState& state,
     }
   }
 
-  // Wait for browser to be ready for connections.
-  bool testing_channel_exists = false;
-  for (int wait_time = 0;
-       wait_time < TestTimeouts::action_max_timeout_ms();
-       wait_time += automation::kSleepTime) {
-    testing_channel_exists = file_util::PathExists(testing_channel_path);
-    if (testing_channel_exists)
-      break;
-    base::PlatformThread::Sleep(automation::kSleepTime);
-  }
-  if (!testing_channel_exists) {
-    LOG(ERROR) << "Failed to wait for testing channel presence.";
-    return false;
+  if (wait_for_server_channel_) {
+    // Wait for browser to be ready for connections.
+    bool testing_channel_exists = false;
+    for (int wait_time = 0;
+         wait_time < TestTimeouts::action_max_timeout_ms();
+         wait_time += automation::kSleepTime) {
+      testing_channel_exists = file_util::PathExists(testing_channel_path);
+      if (testing_channel_exists)
+        break;
+      base::PlatformThread::Sleep(automation::kSleepTime);
+    }
+    if (!testing_channel_exists) {
+      LOG(ERROR) << "Failed to wait for testing channel presence.";
+      return false;
+    }
   }
 
   if (!ConnectToRunningBrowser(wait_for_initial_loads)) {