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

chrome/test/automation/proxy_launcher.h

Index: chrome/test/automation/proxy_launcher.h
diff --git a/chrome/test/automation/proxy_launcher.h b/chrome/test/automation/proxy_launcher.h
index c878719adfd53c668709985f113c8e26ca9675ef..12beeb06e014fe7f4cb7368f7f99c8d51ca84480 100644
--- a/chrome/test/automation/proxy_launcher.h
+++ b/chrome/test/automation/proxy_launcher.h
@@ -65,8 +65,10 @@ class ProxyLauncher {
   virtual ~ProxyLauncher();
 
   // Launches the browser if needed and establishes a connection with it.
-  virtual void InitializeConnection(const LaunchState& state,
-                                    bool wait_for_initial_loads) = 0;
+  // Returns true on success.
+  virtual bool InitializeConnection(
+      const LaunchState& state,
+      bool wait_for_initial_loads) WARN_UNUSED_RESULT = 0;
 
   // Shuts down the browser if needed and destroys any
   // connections established by InitalizeConnection.
@@ -288,8 +290,9 @@ class NamedProxyLauncher : public ProxyLauncher {
                      bool launch_browser, bool disconnect_on_failure);
 
   virtual AutomationProxy* CreateAutomationProxy(int execution_timeout);
-  virtual void InitializeConnection(const LaunchState& state,
-                                    bool wait_for_initial_loads);
+  virtual bool InitializeConnection(
+      const LaunchState& state,
+      bool wait_for_initial_loads) OVERRIDE WARN_UNUSED_RESULT;
   virtual void TerminateConnection();
   virtual std::string PrefixedChannelID() const;
 
@@ -307,8 +310,9 @@ class AnonymousProxyLauncher : public ProxyLauncher {
  public:
   explicit AnonymousProxyLauncher(bool disconnect_on_failure);
   virtual AutomationProxy* CreateAutomationProxy(int execution_timeout);
-  virtual void InitializeConnection(const LaunchState& state,
-                                    bool wait_for_initial_loads);
+  virtual bool InitializeConnection(
+      const LaunchState& state,
+      bool wait_for_initial_loads) OVERRIDE WARN_UNUSED_RESULT;
   virtual void TerminateConnection();
   virtual std::string PrefixedChannelID() const;