Have ChromeDriver return the correct error code for alerts.

Also, don't throw an alert error in set selected if the selection causes
an alert.
BUG=94959
TEST=none


Review URL: http://codereview.chromium.org/8965008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@114874 0039d316-1c4b-4281-b951-d872f2087c98

15 files changed, 462 insertions, 290 deletions

diff --git a/chrome/browser/automation/automation_provider_json.cc b/chrome/browser/automation/automation_provider_json.cc
index 27c8474a..9a5c57f 100644
--- a/chrome/browser/automation/automation_provider_json.cc
+++ b/chrome/browser/automation/automation_provider_json.cc
@@ -16,20 +16,8 @@
 #include "chrome/common/automation_messages.h"
 #include "content/browser/tab_contents/tab_contents.h"
 
-namespace {
-
-// Util for creating a JSON error return string (dict with key
-// 'error' and error string value).  No need to quote input.
-std::string JSONErrorString(const std::string& err) {
-  std::string prefix = "{\"error\": \"";
-  std::string no_quote_err;
-  std::string suffix = "\"}";
-
-  base::JsonDoubleQuote(err, false, &no_quote_err);
-  return prefix + no_quote_err + suffix;
-}
-
-}  // namespace
+using automation::Error;
+using automation::ErrorCode;
 
 AutomationJSONReply::AutomationJSONReply(AutomationProvider* provider,
                                          IPC::Message* reply_message)
@@ -53,10 +41,23 @@ void AutomationJSONReply::SendSuccess(const Value* value) {
 }
 
 void AutomationJSONReply::SendError(const std::string& error_message) {
+  SendErrorInternal(Error(error_message));
+}
+
+void AutomationJSONReply::SendErrorCode(ErrorCode code) {
+  SendErrorInternal(Error(code));
+}
+
+void AutomationJSONReply::SendErrorInternal(const Error& error) {
   DCHECK(message_) << "Resending reply for JSON automation request";
-  std::string json_string = JSONErrorString(error_message);
-  AutomationMsg_SendJSONRequest::WriteReplyParams(
-      message_, json_string, false);
+
+  base::DictionaryValue dict;
+  dict.SetString("error", error.message());
+  dict.SetInteger("code", error.code());
+  std::string json;
+  base::JSONWriter::Write(&dict, false /* pretty_print */, &json);
+
+  AutomationMsg_SendJSONRequest::WriteReplyParams(message_, json, false);
   provider_->Send(message_);
   message_ = NULL;
 }
diff --git a/chrome/browser/automation/automation_provider_json.h b/chrome/browser/automation/automation_provider_json.h
index b7a8674..7b46879 100644
--- a/chrome/browser/automation/automation_provider_json.h
+++ b/chrome/browser/automation/automation_provider_json.h
@@ -11,6 +11,7 @@
 #include <string>
 
 #include "base/compiler_specific.h"
+#include "chrome/common/automation_constants.h"
 
 class AutomationId;
 class AutomationProvider;
@@ -47,7 +48,13 @@ class AutomationJSONReply {
   // Send an error reply along with error message |error_message|.
   void SendError(const std::string& error_message);
 
+  // Send an error reply along with the specified error code and its
+  // associated error message.
+  void SendErrorCode(automation::ErrorCode code);
+
  private:
+  void SendErrorInternal(const automation::Error& error);
+
   AutomationProvider* provider_;
   IPC::Message* message_;
 };
diff --git a/chrome/browser/automation/automation_provider_observers.cc b/chrome/browser/automation/automation_provider_observers.cc
index c1d5be9..2435617 100644
--- a/chrome/browser/automation/automation_provider_observers.cc
+++ b/chrome/browser/automation/automation_provider_observers.cc
@@ -1265,8 +1265,7 @@ void DomOperationMessageSender::OnDomOperationCompleted(
 void DomOperationMessageSender::OnModalDialogShown() {
   if (automation_ && use_json_interface_) {
     AutomationJSONReply(automation_, reply_message_.release())
-        .SendError("Could not complete script execution because a modal "
-                       "dialog is active");
+        .SendErrorCode(automation::kBlockedByModalDialog);
     delete this;
   }
 }
diff --git a/chrome/browser/automation/automation_util.cc b/chrome/browser/automation/automation_util.cc
index 07b6909..a092763 100644
--- a/chrome/browser/automation/automation_util.cc
+++ b/chrome/browser/automation/automation_util.cc
@@ -397,8 +397,8 @@ bool SendErrorIfModalDialogActive(AutomationProvider* provider,
                                   IPC::Message* message) {
   bool active = AppModalDialogQueue::GetInstance()->HasActiveDialog();
   if (active) {
-    AutomationJSONReply(provider, message).SendError(
-        "Command cannot be performed because a modal dialog is active");
+    AutomationJSONReply(provider, message).SendErrorCode(
+        automation::kBlockedByModalDialog);
   }
   return active;
 }
diff --git a/chrome/browser/automation/testing_automation_provider.cc b/chrome/browser/automation/testing_automation_provider.cc
index aa9591f..7068738 100644
--- a/chrome/browser/automation/testing_automation_provider.cc
+++ b/chrome/browser/automation/testing_automation_provider.cc
@@ -145,6 +145,8 @@
 #include "chrome/browser/download/download_shelf.h"
 #endif
 
+using automation::Error;
+using automation::ErrorCode;
 using automation_util::SendErrorIfModalDialogActive;
 using content::BrowserThread;
 using content::ChildProcessHost;
@@ -5741,14 +5743,11 @@ namespace {
 
 // Gets the active JavaScript modal dialog, or NULL if none.
 JavaScriptAppModalDialog* GetActiveJavaScriptModalDialog(
-    std::string* error_msg) {
+    ErrorCode* error_code) {
   AppModalDialogQueue* dialog_queue = AppModalDialogQueue::GetInstance();
-  if (!dialog_queue->HasActiveDialog()) {
-    *error_msg = "No modal dialog is showing";
-    return NULL;
-  }
-  if (!dialog_queue->active_dialog()->IsJavaScriptModalDialog()) {
-    *error_msg = "No JavaScript modal dialog is showing";
+  if (!dialog_queue->HasActiveDialog() ||
+      !dialog_queue->active_dialog()->IsJavaScriptModalDialog()) {
+    *error_code = automation::kNoJavaScriptModalDialogOpen;
     return NULL;
   }
   return static_cast<JavaScriptAppModalDialog*>(dialog_queue->active_dialog());
@@ -5759,10 +5758,10 @@ JavaScriptAppModalDialog* GetActiveJavaScriptModalDialog(
 void TestingAutomationProvider::GetAppModalDialogMessage(
     DictionaryValue* args, IPC::Message* reply_message) {
   AutomationJSONReply reply(this, reply_message);
-  std::string error_msg;
-  JavaScriptAppModalDialog* dialog = GetActiveJavaScriptModalDialog(&error_msg);
+  ErrorCode code;
+  JavaScriptAppModalDialog* dialog = GetActiveJavaScriptModalDialog(&code);
   if (!dialog) {
-    reply.SendError(error_msg);
+    reply.SendErrorCode(code);
     return;
   }
   DictionaryValue result_dict;
@@ -5779,10 +5778,10 @@ void TestingAutomationProvider::AcceptOrDismissAppModalDialog(
     return;
   }
 
-  std::string error_msg;
-  JavaScriptAppModalDialog* dialog = GetActiveJavaScriptModalDialog(&error_msg);
+  ErrorCode code;
+  JavaScriptAppModalDialog* dialog = GetActiveJavaScriptModalDialog(&code);
   if (!dialog) {
-    reply.SendError(error_msg);
+    reply.SendErrorCode(code);
     return;
   }
   if (accept) {
diff --git a/chrome/common/automation_constants.cc b/chrome/common/automation_constants.cc
index f380088..0fbb0de 100644
--- a/chrome/common/automation_constants.cc
+++ b/chrome/common/automation_constants.cc
@@ -21,4 +21,44 @@ const char kNamedInterfacePrefix[] = "NamedTestingInterface:";
 
 const int kChromeDriverAutomationVersion = 1;
 
+namespace {
+
+// Returns the string equivalent of the given |ErrorCode|.
+const char* DefaultMessageForErrorCode(ErrorCode code) {
+  switch (code) {
+    case kUnknownError:
+      return "Unknown error";
+    case kNoJavaScriptModalDialogOpen:
+      return "No JavaScript modal dialog is open";
+    case kBlockedByModalDialog:
+      return "Command blocked by an open modal dialog";
+    default:
+      return "<unknown>";
+  }
+}
+
+}  // namespace
+
+Error::Error() : code_(kUnknownError) { }
+
+Error::Error(ErrorCode code)
+    : code_(code),
+      message_(DefaultMessageForErrorCode(code)) { }
+
+Error::Error(const std::string& error_msg)
+    : code_(kUnknownError), message_(error_msg) { }
+
+Error::Error(ErrorCode code, const std::string& error_msg)
+    : code_(code), message_(error_msg) { }
+
+Error::~Error() { }
+
+ErrorCode Error::code() const {
+  return code_;
+}
+
+const std::string& Error::message() const {
+  return message_;
+}
+
 }  // namespace automation
diff --git a/chrome/common/automation_constants.h b/chrome/common/automation_constants.h
index 1e2cdb3..3754d43 100644
--- a/chrome/common/automation_constants.h
+++ b/chrome/common/automation_constants.h
@@ -6,6 +6,8 @@
 #define CHROME_COMMON_AUTOMATION_CONSTANTS_H__
 #pragma once
 
+#include <string>
+
 namespace automation {
 
 // JSON value labels for proxy settings that are passed in via
@@ -60,6 +62,46 @@ enum MouseButton {
 // TODO(kkania): Investigate a better backwards compatible automation solution.
 extern const int kChromeDriverAutomationVersion;
 
+// Automation error codes. These provide the client a simple way
+// to detect certain types of errors it may be interested in handling.
+// The error code values must stay consistent across compatible versions.
+enum ErrorCode {
+  // An unknown error occurred.
+  kUnknownError = 0,
+  // Trying to operate on a JavaScript modal dialog when none is open.
+  kNoJavaScriptModalDialogOpen = 1,
+  // An open modal dialog blocked the operation. The operation may have
+  // partially completed.
+  kBlockedByModalDialog = 2,
+};
+
+// Represents an automation error. Each error has a code and an error message.
+class Error {
+ public:
+  // Creates an invalid error.
+  Error();
+
+  // Creates an error for the given code. A default message for the given code
+  // will be used as the error message.
+  explicit Error(ErrorCode code);
+
+  // Creates an error for the given message. The |kUnknownError| type will
+  // be used.
+  explicit Error(const std::string& error_msg);
+
+  // Creates an error for the given code and message.
+  Error(ErrorCode code, const std::string& error_msg);
+
+  virtual ~Error();
+
+  ErrorCode code() const;
+  const std::string& message() const;
+
+ private:
+  ErrorCode code_;
+  std::string message_;
+};
+
 }  // namespace automation
 
 // Used by AutomationProxy, declared here so that other headers don't need
diff --git a/chrome/test/automation/automation_json_requests.cc b/chrome/test/automation/automation_json_requests.cc
index 4dd8478..0c624527 100644
--- a/chrome/test/automation/automation_json_requests.cc
+++ b/chrome/test/automation/automation_json_requests.cc
@@ -18,6 +18,8 @@
 #include "chrome/common/automation_messages.h"
 #include "chrome/test/automation/automation_proxy.h"
 
+using automation::Error;
+using automation::ErrorCode;
 using base::DictionaryValue;
 using base::ListValue;
 
@@ -26,7 +28,7 @@ namespace {
 bool SendAutomationJSONRequest(AutomationMessageSender* sender,
                                const DictionaryValue& request_dict,
                                DictionaryValue* reply_dict,
-                               std::string* error_msg) {
+                               Error* error) {
   std::string request, reply;
   base::JSONWriter::Write(&request_dict, false, &request);
   std::string command;
@@ -37,27 +39,29 @@ bool SendAutomationJSONRequest(AutomationMessageSender* sender,
   bool success = false;
   if (!SendAutomationJSONRequestWithDefaultTimeout(
           sender, request, &reply, &success)) {
-    *error_msg = base::StringPrintf(
+    *error = Error(base::StringPrintf(
         "Chrome did not respond to '%s'. Elapsed time was %" PRId64 " ms.",
         command.c_str(),
-        (base::Time::Now() - before_sending).InMilliseconds());
+        (base::Time::Now() - before_sending).InMilliseconds()));
+    LOG(INFO) << error->message();
     return false;
   }
   scoped_ptr<Value> value(base::JSONReader::Read(reply, true));
   if (!value.get() || !value->IsType(Value::TYPE_DICTIONARY)) {
+    *error = Error("JSON request did not return a dictionary");
     LOG(ERROR) << "JSON request did not return dict: " << command << "\n";
     return false;
   }
   DictionaryValue* dict = static_cast<DictionaryValue*>(value.get());
   if (!success) {
-    std::string error;
-    dict->GetString("error", &error);
-    *error_msg = base::StringPrintf(
-        "Internal Chrome error during '%s': (%s).",
-        command.c_str(),
-        error.c_str());
-    LOG(ERROR) << "JSON request failed: " << command << "\n"
-               << "    with error: " << error;
+    std::string error_msg;
+    dict->GetString("error", &error_msg);
+    int int_code = automation::kUnknownError;
+    dict->GetInteger("code", &int_code);
+    ErrorCode code = static_cast<ErrorCode>(int_code);
+    *error = Error(code, error_msg);
+    LOG(INFO) << "JSON request failed: " << command << "\n"
+              << "    with error: " << error_msg;
     return false;
   }
   reply_dict->MergeDictionary(dict);
@@ -203,12 +207,12 @@ bool SendGetIndicesFromTabIdJSONRequest(
     int tab_id,
     int* browser_index,
     int* tab_index,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue request_dict;
   request_dict.SetString("command", "GetIndicesFromTab");
   request_dict.SetInteger("tab_id", tab_id);
   DictionaryValue reply_dict;
-  if (!SendAutomationJSONRequest(sender, request_dict, &reply_dict, error_msg))
+  if (!SendAutomationJSONRequest(sender, request_dict, &reply_dict, error))
     return false;
   if (!reply_dict.GetInteger("windex", browser_index))
     return false;
@@ -222,12 +226,12 @@ bool SendGetIndicesFromTabHandleJSONRequest(
     int tab_handle,
     int* browser_index,
     int* tab_index,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue request_dict;
   request_dict.SetString("command", "GetIndicesFromTab");
   request_dict.SetInteger("tab_handle", tab_handle);
   DictionaryValue reply_dict;
-  if (!SendAutomationJSONRequest(sender, request_dict, &reply_dict, error_msg))
+  if (!SendAutomationJSONRequest(sender, request_dict, &reply_dict, error))
     return false;
   if (!reply_dict.GetInteger("windex", browser_index))
     return false;
@@ -242,14 +246,14 @@ bool SendNavigateToURLJSONRequest(
     const std::string& url,
     int navigation_count,
     AutomationMsg_NavigationResponseValues* nav_response,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "NavigateToURL");
   locator.UpdateDictionary(&dict, "auto_id");
   dict.SetString("url", url);
   dict.SetInteger("navigation_count", navigation_count);
   DictionaryValue reply_dict;
-  if (!SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg))
+  if (!SendAutomationJSONRequest(sender, dict, &reply_dict, error))
     return false;
   int response = 0;
   if (!reply_dict.GetInteger("result", &response))
@@ -264,14 +268,14 @@ bool SendExecuteJavascriptJSONRequest(
     const std::string& frame_xpath,
     const std::string& javascript,
     Value** result,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "ExecuteJavascript");
   locator.UpdateDictionary(&dict, "auto_id");
   dict.SetString("frame_xpath", frame_xpath);
   dict.SetString("javascript", javascript);
   DictionaryValue reply_dict;
-  if (!SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg))
+  if (!SendAutomationJSONRequest(sender, dict, &reply_dict, error))
     return false;
 
   std::string json;
@@ -297,60 +301,60 @@ bool SendExecuteJavascriptJSONRequest(
 bool SendGoForwardJSONRequest(
     AutomationMessageSender* sender,
     const WebViewLocator& locator,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "GoForward");
   locator.UpdateDictionary(&dict, "auto_id");
   DictionaryValue reply_dict;
-  return SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg);
+  return SendAutomationJSONRequest(sender, dict, &reply_dict, error);
 }
 
 bool SendGoBackJSONRequest(
     AutomationMessageSender* sender,
     const WebViewLocator& locator,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "GoBack");
   locator.UpdateDictionary(&dict, "auto_id");
   DictionaryValue reply_dict;
-  return SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg);
+  return SendAutomationJSONRequest(sender, dict, &reply_dict, error);
 }
 
 bool SendReloadJSONRequest(
     AutomationMessageSender* sender,
     const WebViewLocator& locator,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "Reload");
   locator.UpdateDictionary(&dict, "auto_id");
   DictionaryValue reply_dict;
-  return SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg);
+  return SendAutomationJSONRequest(sender, dict, &reply_dict, error);
 }
 
 bool SendCaptureEntirePageJSONRequest(
     AutomationMessageSender* sender,
     const WebViewLocator& locator,
     const FilePath& path,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "CaptureEntirePage");
   locator.UpdateDictionary(&dict, "auto_id");
   dict.SetString("path", path.value());
   DictionaryValue reply_dict;
 
-  return SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg);
+  return SendAutomationJSONRequest(sender, dict, &reply_dict, error);
 }
 
 bool SendGetCookiesJSONRequest(
     AutomationMessageSender* sender,
     const std::string& url,
     ListValue** cookies,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "GetCookies");
   dict.SetString("url", url);
   DictionaryValue reply_dict;
-  if (!SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg))
+  if (!SendAutomationJSONRequest(sender, dict, &reply_dict, error))
     return false;
   Value* cookies_unscoped_value;
   if (!reply_dict.Remove("cookies", &cookies_unscoped_value))
@@ -366,43 +370,43 @@ bool SendDeleteCookieJSONRequest(
     AutomationMessageSender* sender,
     const std::string& url,
     const std::string& cookie_name,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "DeleteCookie");
   dict.SetString("url", url);
   dict.SetString("name", cookie_name);
   DictionaryValue reply_dict;
-  return SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg);
+  return SendAutomationJSONRequest(sender, dict, &reply_dict, error);
 }
 
 bool SendSetCookieJSONRequest(
     AutomationMessageSender* sender,
     const std::string& url,
     DictionaryValue* cookie_dict,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "SetCookie");
   dict.SetString("url", url);
   dict.Set("cookie", cookie_dict->DeepCopy());
   DictionaryValue reply_dict;
-  return SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg);
+  return SendAutomationJSONRequest(sender, dict, &reply_dict, error);
 }
 
 bool SendGetTabIdsJSONRequest(
     AutomationMessageSender* sender,
     std::vector<WebViewInfo>* views,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "GetTabIds");
   DictionaryValue reply_dict;
-  if (!SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg))
+  if (!SendAutomationJSONRequest(sender, dict, &reply_dict, error))
     return false;
   ListValue* id_list;
   if (reply_dict.GetList("ids", &id_list)) {
     for (size_t i = 0; i < id_list->GetSize(); ++i) {
       int id;
       if (!id_list->GetInteger(i, &id)) {
-        *error_msg = "Returned id in 'tab_ids' is not an integer";
+        *error = Error("Returned id in 'tab_ids' is not an integer");
         return false;
       }
       views->push_back(WebViewInfo(
@@ -415,27 +419,30 @@ bool SendGetTabIdsJSONRequest(
 bool SendGetWebViewsJSONRequest(
     AutomationMessageSender* sender,
     std::vector<WebViewInfo>* views,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "GetViews");
   DictionaryValue reply_dict;
-  if (!SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg))
+  if (!SendAutomationJSONRequest(sender, dict, &reply_dict, error))
     return false;
   ListValue* views_list;
   if (!reply_dict.GetList("views", &views_list)) {
-    *error_msg = "Returned 'views' key is missing or invalid";
+    *error = Error("Returned 'views' key is missing or invalid");
     return false;
   }
   for (size_t i = 0; i < views_list->GetSize(); ++i) {
     DictionaryValue* view_dict;
     if (!views_list->GetDictionary(i, &view_dict)) {
-      *error_msg = "Returned 'views' key contains non-dictionary values";
+      *error = Error("Returned 'views' key contains non-dictionary values");
       return false;
     }
     AutomationId view_id;
+    std::string error_msg;
     if (!AutomationId::FromValueInDictionary(
-            view_dict, "auto_id", &view_id, error_msg))
+            view_dict, "auto_id", &view_id, &error_msg)) {
+      *error = Error(error_msg);
       return false;
+    }
     std::string extension_id;
     view_dict->GetString("extension_id", &extension_id);
     views->push_back(WebViewInfo(
@@ -448,12 +455,12 @@ bool SendIsTabIdValidJSONRequest(
     AutomationMessageSender* sender,
     const WebViewId& view_id,
     bool* is_valid,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "IsTabIdValid");
   view_id.UpdateDictionary(&dict, "tab_id");
   DictionaryValue reply_dict;
-  if (!SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg))
+  if (!SendAutomationJSONRequest(sender, dict, &reply_dict, error))
     return false;
   return reply_dict.GetBoolean("is_valid", is_valid);
 }
@@ -462,12 +469,12 @@ bool SendDoesAutomationObjectExistJSONRequest(
     AutomationMessageSender* sender,
     const WebViewId& view_id,
     bool* does_exist,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "DoesAutomationObjectExist");
   view_id.UpdateDictionary(&dict, "auto_id");
   DictionaryValue reply_dict;
-  if (!SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg))
+  if (!SendAutomationJSONRequest(sender, dict, &reply_dict, error))
     return false;
   return reply_dict.GetBoolean("does_exist", does_exist);
 }
@@ -475,12 +482,12 @@ bool SendDoesAutomationObjectExistJSONRequest(
 bool SendCloseViewJSONRequest(
     AutomationMessageSender* sender,
     const WebViewLocator& locator,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "CloseTab");
   locator.UpdateDictionary(&dict, "auto_id");
   DictionaryValue reply_dict;
-  return SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg);
+  return SendAutomationJSONRequest(sender, dict, &reply_dict, error);
 }
 
 bool SendMouseMoveJSONRequest(
@@ -488,14 +495,14 @@ bool SendMouseMoveJSONRequest(
     const WebViewLocator& locator,
     int x,
     int y,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "WebkitMouseMove");
   locator.UpdateDictionary(&dict, "auto_id");
   dict.SetInteger("x", x);
   dict.SetInteger("y", y);
   DictionaryValue reply_dict;
-  return SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg);
+  return SendAutomationJSONRequest(sender, dict, &reply_dict, error);
 }
 
 bool SendMouseClickJSONRequest(
@@ -504,7 +511,7 @@ bool SendMouseClickJSONRequest(
     automation::MouseButton button,
     int x,
     int y,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "WebkitMouseClick");
   locator.UpdateDictionary(&dict, "auto_id");
@@ -512,7 +519,7 @@ bool SendMouseClickJSONRequest(
   dict.SetInteger("x", x);
   dict.SetInteger("y", y);
   DictionaryValue reply_dict;
-  return SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg);
+  return SendAutomationJSONRequest(sender, dict, &reply_dict, error);
 }
 
 bool SendMouseDragJSONRequest(
@@ -522,7 +529,7 @@ bool SendMouseDragJSONRequest(
     int start_y,
     int end_x,
     int end_y,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "WebkitMouseDrag");
   locator.UpdateDictionary(&dict, "auto_id");
@@ -531,7 +538,7 @@ bool SendMouseDragJSONRequest(
   dict.SetInteger("end_x", end_x);
   dict.SetInteger("end_y", end_y);
   DictionaryValue reply_dict;
-  return SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg);
+  return SendAutomationJSONRequest(sender, dict, &reply_dict, error);
 }
 
 bool SendMouseButtonDownJSONRequest(
@@ -539,14 +546,14 @@ bool SendMouseButtonDownJSONRequest(
     const WebViewLocator& locator,
     int x,
     int y,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "WebkitMouseButtonDown");
   locator.UpdateDictionary(&dict, "auto_id");
   dict.SetInteger("x", x);
   dict.SetInteger("y", y);
   DictionaryValue reply_dict;
-  return SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg);
+  return SendAutomationJSONRequest(sender, dict, &reply_dict, error);
 }
 
 bool SendMouseButtonUpJSONRequest(
@@ -554,14 +561,14 @@ bool SendMouseButtonUpJSONRequest(
     const WebViewLocator& locator,
     int x,
     int y,
-    std::string* error_msg)  {
+    Error* error)  {
   DictionaryValue dict;
   dict.SetString("command", "WebkitMouseButtonUp");
   locator.UpdateDictionary(&dict, "auto_id");
   dict.SetInteger("x", x);
   dict.SetInteger("y", y);
   DictionaryValue reply_dict;
-  return SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg);
+  return SendAutomationJSONRequest(sender, dict, &reply_dict, error);
 }
 
 bool SendMouseDoubleClickJSONRequest(
@@ -569,21 +576,21 @@ bool SendMouseDoubleClickJSONRequest(
     const WebViewLocator& locator,
     int x,
     int y,
-    std::string* error_msg)  {
+    Error* error)  {
   DictionaryValue dict;
   dict.SetString("command", "WebkitMouseDoubleClick");
   locator.UpdateDictionary(&dict, "auto_id");
   dict.SetInteger("x", x);
   dict.SetInteger("y", y);
   DictionaryValue reply_dict;
-  return SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg);
+  return SendAutomationJSONRequest(sender, dict, &reply_dict, error);
 }
 
 bool SendWebKeyEventJSONRequest(
     AutomationMessageSender* sender,
     const WebViewLocator& locator,
     const WebKeyEvent& key_event,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "SendWebkitKeyEvent");
   locator.UpdateDictionary(&dict, "auto_id");
@@ -595,7 +602,7 @@ bool SendWebKeyEventJSONRequest(
   dict.SetInteger("modifiers", key_event.modifiers);
   dict.SetBoolean("isSystemKey", false);
   DictionaryValue reply_dict;
-  return SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg);
+  return SendAutomationJSONRequest(sender, dict, &reply_dict, error);
 }
 
 bool SendNativeKeyEventJSONRequest(
@@ -603,14 +610,14 @@ bool SendNativeKeyEventJSONRequest(
     const WebViewLocator& locator,
     ui::KeyboardCode key_code,
     int modifiers,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "SendOSLevelKeyEventToTab");
   locator.UpdateDictionary(&dict, "auto_id");
   dict.SetInteger("keyCode", key_code);
   dict.SetInteger("modifiers", modifiers);
   DictionaryValue reply_dict;
-  return SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg);
+  return SendAutomationJSONRequest(sender, dict, &reply_dict, error);
 }
 
 bool SendDragAndDropFilePathsJSONRequest(
@@ -619,7 +626,7 @@ bool SendDragAndDropFilePathsJSONRequest(
     int x,
     int y,
     const std::vector<FilePath::StringType>& paths,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "DragAndDropFilePaths");
   locator.UpdateDictionary(&dict, "auto_id");
@@ -633,17 +640,17 @@ bool SendDragAndDropFilePathsJSONRequest(
   dict.Set("paths", list_value);
 
   DictionaryValue reply_dict;
-  return SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg);
+  return SendAutomationJSONRequest(sender, dict, &reply_dict, error);
 }
 
 bool SendGetAppModalDialogMessageJSONRequest(
     AutomationMessageSender* sender,
     std::string* message,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "GetAppModalDialogMessage");
   DictionaryValue reply_dict;
-  if (!SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg))
+  if (!SendAutomationJSONRequest(sender, dict, &reply_dict, error))
     return false;
   return reply_dict.GetString("message", message);
 }
@@ -651,43 +658,43 @@ bool SendGetAppModalDialogMessageJSONRequest(
 bool SendAcceptOrDismissAppModalDialogJSONRequest(
     AutomationMessageSender* sender,
     bool accept,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "AcceptOrDismissAppModalDialog");
   dict.SetBoolean("accept", accept);
   DictionaryValue reply_dict;
-  return SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg);
+  return SendAutomationJSONRequest(sender, dict, &reply_dict, error);
 }
 
 bool SendAcceptPromptAppModalDialogJSONRequest(
     AutomationMessageSender* sender,
     const std::string& prompt_text,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "AcceptOrDismissAppModalDialog");
   dict.SetBoolean("accept", true);
   dict.SetString("prompt_text", prompt_text);
   DictionaryValue reply_dict;
-  return SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg);
+  return SendAutomationJSONRequest(sender, dict, &reply_dict, error);
 }
 
 bool SendWaitForAllViewsToStopLoadingJSONRequest(
     AutomationMessageSender* sender,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "WaitForAllTabsToStopLoading");
   DictionaryValue reply_dict;
-  return SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg);
+  return SendAutomationJSONRequest(sender, dict, &reply_dict, error);
 }
 
 bool SendGetChromeDriverAutomationVersion(
     AutomationMessageSender* sender,
     int* version,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "GetChromeDriverAutomationVersion");
   DictionaryValue reply_dict;
-  if (!SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg))
+  if (!SendAutomationJSONRequest(sender, dict, &reply_dict, error))
     return false;
   return reply_dict.GetInteger("version", version);
 }
@@ -697,16 +704,16 @@ bool SendInstallExtensionJSONRequest(
     const FilePath& path,
     bool with_ui,
     std::string* extension_id,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "InstallExtension");
   dict.SetString("path", path.value());
   dict.SetBoolean("with_ui", with_ui);
   DictionaryValue reply_dict;
-  if (!SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg))
+  if (!SendAutomationJSONRequest(sender, dict, &reply_dict, error))
     return false;
   if (!reply_dict.GetString("id", extension_id)) {
-    *error_msg = "Missing or invalid 'id'";
+    *error = Error("Missing or invalid 'id'");
     return false;
   }
   return true;
@@ -715,15 +722,15 @@ bool SendInstallExtensionJSONRequest(
 bool SendGetExtensionsInfoJSONRequest(
     AutomationMessageSender* sender,
     ListValue* extensions_list,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "GetExtensionsInfo");
   DictionaryValue reply_dict;
-  if (!SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg))
+  if (!SendAutomationJSONRequest(sender, dict, &reply_dict, error))
     return false;
   ListValue* extensions_list_swap;
   if (!reply_dict.GetList("extensions", &extensions_list_swap)) {
-    *error_msg = "Missing or invalid 'extensions'";
+    *error = Error("Missing or invalid 'extensions'");
     return false;
   }
   extensions_list->Swap(extensions_list_swap);
@@ -735,16 +742,16 @@ bool SendIsPageActionVisibleJSONRequest(
     const WebViewId& tab_id,
     const std::string& extension_id,
     bool* is_visible,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "IsPageActionVisible");
   tab_id.UpdateDictionary(&dict, "auto_id");
   dict.SetString("extension_id", extension_id);
   DictionaryValue reply_dict;
-  if (!SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg))
+  if (!SendAutomationJSONRequest(sender, dict, &reply_dict, error))
     return false;
   if (!reply_dict.GetBoolean("is_visible", is_visible)) {
-    *error_msg = "Missing or invalid 'is_visible'";
+    *error = Error("Missing or invalid 'is_visible'");
     return false;
   }
   return true;
@@ -755,21 +762,21 @@ bool SendSetExtensionStateJSONRequest(
     const std::string& extension_id,
     bool enable,
     bool allow_in_incognito,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "SetExtensionStateById");
   dict.SetString("id", extension_id);
   dict.SetBoolean("enable", enable);
   dict.SetBoolean("allow_in_incognito", allow_in_incognito);
   DictionaryValue reply_dict;
-  return SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg);
+  return SendAutomationJSONRequest(sender, dict, &reply_dict, error);
 }
 
 bool SendClickExtensionButtonJSONRequest(
     AutomationMessageSender* sender,
     const std::string& extension_id,
     bool browser_action,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   if (browser_action)
     dict.SetString("command", "TriggerBrowserActionById");
@@ -779,26 +786,26 @@ bool SendClickExtensionButtonJSONRequest(
   dict.SetInteger("windex", 0);
   dict.SetInteger("tab_index", 0);
   DictionaryValue reply_dict;
-  return SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg);
+  return SendAutomationJSONRequest(sender, dict, &reply_dict, error);
 }
 
 bool SendUninstallExtensionJSONRequest(
     AutomationMessageSender* sender,
     const std::string& extension_id,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "UninstallExtensionById");
   dict.SetString("id", extension_id);
   DictionaryValue reply_dict;
-  if (!SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg))
+  if (!SendAutomationJSONRequest(sender, dict, &reply_dict, error))
     return false;
   bool success;
   if (!reply_dict.GetBoolean("success", &success)) {
-    *error_msg = "Missing or invalid 'success'";
+    *error = Error("Missing or invalid 'success'");
     return false;
   }
   if (!success) {
-    *error_msg = "Extension uninstall not permitted";
+    *error = Error("Extension uninstall not permitted");
     return false;
   }
   return true;
@@ -808,25 +815,25 @@ bool SendSetLocalStatePreferenceJSONRequest(
     AutomationMessageSender* sender,
     const std::string& pref,
     base::Value* value,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "SetLocalStatePrefs");
   dict.SetString("path", pref);
   dict.Set("value", value);
   DictionaryValue reply_dict;
-  return SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg);
+  return SendAutomationJSONRequest(sender, dict, &reply_dict, error);
 }
 
 bool SendSetPreferenceJSONRequest(
     AutomationMessageSender* sender,
     const std::string& pref,
     base::Value* value,
-    std::string* error_msg) {
+    Error* error) {
   DictionaryValue dict;
   dict.SetString("command", "SetPrefs");
   dict.SetInteger("windex", 0);
   dict.SetString("path", pref);
   dict.Set("value", value);
   DictionaryValue reply_dict;
-  return SendAutomationJSONRequest(sender, dict, &reply_dict, error_msg);
+  return SendAutomationJSONRequest(sender, dict, &reply_dict, error);
 }
diff --git a/chrome/test/automation/automation_json_requests.h b/chrome/test/automation/automation_json_requests.h
index 89b1072..4d855b1 100644
--- a/chrome/test/automation/automation_json_requests.h
+++ b/chrome/test/automation/automation_json_requests.h
@@ -170,7 +170,7 @@ bool SendGetIndicesFromTabIdJSONRequest(
     int tab_id,
     int* browser_index,
     int* tab_index,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests the current browser and tab indices for the given |TabProxy|
 // handle. Returns true on success.
@@ -179,7 +179,7 @@ bool SendGetIndicesFromTabHandleJSONRequest(
     int tab_proxy_handle,
     int* browser_index,
     int* tab_index,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests to navigate to the given url and wait for the given number of
 // navigations to complete. Returns true on success.
@@ -189,7 +189,7 @@ bool SendNavigateToURLJSONRequest(
     const std::string& url,
     int navigation_count,
     AutomationMsg_NavigationResponseValues* nav_response,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests the given javascript to be executed in the frame specified by the
 // given xpath. Returns true on success. If true, |result| will be set to the
@@ -200,28 +200,28 @@ bool SendExecuteJavascriptJSONRequest(
     const std::string& frame_xpath,
     const std::string& javascript,
     base::Value** result,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests the specified view to go forward. Waits for the load to complete.
 // Returns true on success.
 bool SendGoForwardJSONRequest(
     AutomationMessageSender* sender,
     const WebViewLocator& locator,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests the specified view to go back. Waits for the load to complete.
 // Returns true on success.
 bool SendGoBackJSONRequest(
     AutomationMessageSender* sender,
     const WebViewLocator& locator,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests the specified view to reload. Waits for the load to complete.
 // Returns true on success.
 bool SendReloadJSONRequest(
     AutomationMessageSender* sender,
     const WebViewLocator& locator,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests a snapshot of the entire page to be saved to the given path
 // in PNG format.
@@ -230,7 +230,7 @@ bool SendCaptureEntirePageJSONRequest(
     AutomationMessageSender* sender,
     const WebViewLocator& locator,
     const FilePath& path,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests all the cookies for the given URL. On success returns true and
 // caller takes ownership of |cookies|, which is a list of all the cookies in
@@ -239,7 +239,7 @@ bool SendGetCookiesJSONRequest(
     AutomationMessageSender* sender,
     const std::string& url,
     base::ListValue** cookies,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests deletion of the cookie with the given name and URL. Returns true
 // on success.
@@ -247,7 +247,7 @@ bool SendDeleteCookieJSONRequest(
     AutomationMessageSender* sender,
     const std::string& url,
     const std::string& cookie_name,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests setting the given cookie for the given URL. Returns true on
 // success. The caller retains ownership of |cookie_dict|.
@@ -255,26 +255,26 @@ bool SendSetCookieJSONRequest(
     AutomationMessageSender* sender,
     const std::string& url,
     base::DictionaryValue* cookie_dict,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests the IDs for all open tabs. Returns true on success.
 bool SendGetTabIdsJSONRequest(
     AutomationMessageSender* sender,
     std::vector<WebViewInfo>* views,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests info for all open views. Returns true on success.
 bool SendGetWebViewsJSONRequest(
     AutomationMessageSender* sender,
     std::vector<WebViewInfo>* views,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests whether the given tab ID is valid. Returns true on success.
 bool SendIsTabIdValidJSONRequest(
     AutomationMessageSender* sender,
     const WebViewId& view_id,
     bool* is_valid,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests whether the given automation ID refers to an actual automation
 // object. Returns true on success.
@@ -282,13 +282,13 @@ bool SendDoesAutomationObjectExistJSONRequest(
     AutomationMessageSender* sender,
     const WebViewId& view_id,
     bool* does_exist,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests to close the given view. Returns true on success.
 bool SendCloseViewJSONRequest(
     AutomationMessageSender* sender,
     const WebViewLocator& locator,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests to send the WebKit event for a mouse move to the given
 // coordinate in the specified view. Returns true on success.
@@ -297,7 +297,7 @@ bool SendMouseMoveJSONRequest(
     const WebViewLocator& locator,
     int x,
     int y,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests to send the WebKit events for a mouse click at the given
 // coordinate in the specified view. Returns true on success.
@@ -307,7 +307,7 @@ bool SendMouseClickJSONRequest(
     automation::MouseButton button,
     int x,
     int y,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests to send the WebKit events for a mouse drag from the start to end
 // coordinates given in the specified view. Returns true on success.
@@ -318,7 +318,7 @@ bool SendMouseDragJSONRequest(
     int start_y,
     int end_x,
     int end_y,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests to send the WebKit event for a mouse button down at the given
 // coordinate in the specified view. Returns true on success.
@@ -327,7 +327,7 @@ bool SendMouseButtonDownJSONRequest(
     const WebViewLocator& locator,
     int x,
     int y,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests to send the WebKit event for a mouse button up at the given
 // coordinate in the specified view. Returns true on success.
@@ -336,7 +336,7 @@ bool SendMouseButtonUpJSONRequest(
     const WebViewLocator& locator,
     int x,
     int y,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests to send the WebKit event for a mouse double click at the given
 // coordinate in the specified view. Returns true on success.
@@ -345,7 +345,7 @@ bool SendMouseDoubleClickJSONRequest(
     const WebViewLocator& locator,
     int x,
     int y,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests to send the WebKit event for the given |WebKeyEvent| in a
 // specified view. Returns true on success.
@@ -353,7 +353,7 @@ bool SendWebKeyEventJSONRequest(
     AutomationMessageSender* sender,
     const WebViewLocator& locator,
     const WebKeyEvent& key_event,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests to send the key event for the given keycode+modifiers to a
 // browser window containing the specified view. Returns true on success.
@@ -362,7 +362,7 @@ bool SendNativeKeyEventJSONRequest(
     const WebViewLocator& locator,
     ui::KeyboardCode key_code,
     int modifiers,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests to drag and drop the file paths at the given coordinate in the
 // specified view. Returns true on success.
@@ -372,40 +372,40 @@ bool SendDragAndDropFilePathsJSONRequest(
     int x,
     int y,
     const std::vector<FilePath::StringType>& paths,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests to get the active JavaScript modal dialog's message. Returns true
 // on success.
 bool SendGetAppModalDialogMessageJSONRequest(
     AutomationMessageSender* sender,
     std::string* message,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests to accept or dismiss the active JavaScript modal dialog.
 // Returns true on success.
 bool SendAcceptOrDismissAppModalDialogJSONRequest(
     AutomationMessageSender* sender,
     bool accept,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests to accept the active JavaScript modal dialog with the given prompt
 // text. Returns true on success.
 bool SendAcceptPromptAppModalDialogJSONRequest(
     AutomationMessageSender* sender,
     const std::string& prompt_text,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests to wait for all views to stop loading. Returns true on success.
 bool SendWaitForAllViewsToStopLoadingJSONRequest(
     AutomationMessageSender* sender,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests the version of ChromeDriver automation supported by the automation
 // server. Returns true on success.
 bool SendGetChromeDriverAutomationVersion(
     AutomationMessageSender* sender,
     int* version,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests that the given extension be installed. If |with_ui| is false,
 // the extension will be installed silently. Returns true on success.
@@ -414,13 +414,13 @@ bool SendInstallExtensionJSONRequest(
     const FilePath& path,
     bool with_ui,
     std::string* extension_id,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests info about all installed extensions. Returns true on success.
 bool SendGetExtensionsInfoJSONRequest(
     AutomationMessageSender* sender,
     base::ListValue* extensions_list,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests whether the given extension's page action is visible in the
 // given tab.
@@ -429,7 +429,7 @@ bool SendIsPageActionVisibleJSONRequest(
     const WebViewId& tab_id,
     const std::string& extension_id,
     bool* is_visible,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests a modification of the given extension state. Returns true on
 // success.
@@ -438,7 +438,7 @@ bool SendSetExtensionStateJSONRequest(
     const std::string& extension_id,
     bool enable,
     bool allow_in_incognito,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests the given extension's action button be pressed. Returns true on
 // success.
@@ -446,13 +446,13 @@ bool SendClickExtensionButtonJSONRequest(
     AutomationMessageSender* sender,
     const std::string& extension_id,
     bool browser_action,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests the given extension be uninstalled. Returns true on success.
 bool SendUninstallExtensionJSONRequest(
     AutomationMessageSender* sender,
     const std::string& extension_id,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests the local state preference to be set to the given value.
 // Ownership of |value| is taken by this function. Returns true on success.
@@ -460,7 +460,7 @@ bool SendSetLocalStatePreferenceJSONRequest(
     AutomationMessageSender* sender,
     const std::string& pref,
     base::Value* value,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 // Requests the user preference to be set to the given value.
 // Ownership of |value| is taken by this function. Returns true on success.
@@ -468,6 +468,6 @@ bool SendSetPreferenceJSONRequest(
     AutomationMessageSender* sender,
     const std::string& pref,
     base::Value* value,
-    std::string* error_msg) WARN_UNUSED_RESULT;
+    automation::Error* error) WARN_UNUSED_RESULT;
 
 #endif  // CHROME_TEST_AUTOMATION_AUTOMATION_JSON_REQUESTS_H_
diff --git a/chrome/test/automation/tab_proxy.cc b/chrome/test/automation/tab_proxy.cc
index b24c23c..094fee3 100644
--- a/chrome/test/automation/tab_proxy.cc
+++ b/chrome/test/automation/tab_proxy.cc
@@ -11,6 +11,7 @@
 #include "base/string16.h"
 #include "base/threading/platform_thread.h"
 #include "base/utf_string_conversions.h"
+#include "chrome/common/automation_constants.h"
 #include "chrome/common/automation_messages.h"
 #include "chrome/test/automation/automation_json_requests.h"
 #include "chrome/test/automation/automation_proxy.h"
@@ -723,15 +724,15 @@ bool TabProxy::CaptureEntirePageAsPNG(const FilePath& path) {
     return false;
 
   int browser_index, tab_index;
-  std::string error_msg;
+  automation::Error error;
   if (!SendGetIndicesFromTabHandleJSONRequest(
-         sender_, handle_, &browser_index, &tab_index, &error_msg)) {
+         sender_, handle_, &browser_index, &tab_index, &error)) {
     return false;
   }
 
   return SendCaptureEntirePageJSONRequest(
       sender_, WebViewLocator::ForIndexPair(browser_index, tab_index),
-      path, &error_msg);
+      path, &error);
 }
 
 #if defined(OS_WIN) && !defined(USE_AURA)
diff --git a/chrome/test/webdriver/test/chromedriver_tests.py b/chrome/test/webdriver/test/chromedriver_tests.py
index cae9772..1666f5a 100644
--- a/chrome/test/webdriver/test/chromedriver_tests.py
+++ b/chrome/test/webdriver/test/chromedriver_tests.py
@@ -815,6 +815,18 @@ class AlertTest(ChromeDriverTest):
     driver.get(self.GetTestDataUrl() + '/alerts.html')
     self.assertRaises(WebDriverException, driver.execute_script, 'alert("ok")')
 
+  # See http://code.google.com/p/selenium/issues/detail?id=2671.
+  def testCanPerformJSBasedActionsThatCauseAlertsAtTheEnd(self):
+    driver = self.GetNewDriver()
+    driver.execute_script(
+        'var select = document.createElement("select");' +
+        'select.innerHTML = "<option>1</option><option>2</option>";' +
+        'select.addEventListener("change", function() { alert("hi"); });' +
+        'document.body.appendChild(select);')
+
+    # Shouldn't throw an exception, even though an alert appears mid-script.
+    driver.find_elements_by_tag_name('option')[-1].click()
+
   def testMustHandleAlertFirst(self):
     driver = self.GetNewDriver()
     driver.get(self.GetTestDataUrl() + '/alerts.html')
diff --git a/chrome/test/webdriver/webdriver_automation.cc b/chrome/test/webdriver/webdriver_automation.cc
index 7334c16..80e25c5 100644
--- a/chrome/test/webdriver/webdriver_automation.cc
+++ b/chrome/test/webdriver/webdriver_automation.cc
@@ -286,10 +286,10 @@ void Automation::Init(const BrowserOptions& options, Error** error) {
   // Check the version of Chrome is compatible with this ChromeDriver.
   chrome_details += ", version (" + automation()->server_version() + ")";
   int version = 0;
-  std::string error_msg;
+  automation::Error auto_error;
   if (!SendGetChromeDriverAutomationVersion(
-          automation(), &version, &error_msg)) {
-    *error = new Error(kUnknownError, error_msg + " " + chrome_details);
+          automation(), &version, &auto_error)) {
+    *error = Error::FromAutomationError(auto_error);
     return;
   }
   if (version > automation::kChromeDriverAutomationVersion) {
@@ -335,11 +335,11 @@ void Automation::ExecuteScript(const WebViewId& view_id,
     return;
 
   Value* unscoped_value;
-  std::string error_msg;
+  automation::Error auto_error;
   if (!SendExecuteJavascriptJSONRequest(automation(), view_locator,
                                         frame_path.value(), script,
-                                        &unscoped_value, &error_msg)) {
-    *error = new Error(kUnknownError, error_msg);
+                                        &unscoped_value, &auto_error)) {
+    *error = Error::FromAutomationError(auto_error);
     return;
   }
   scoped_ptr<Value> value(unscoped_value);
@@ -355,11 +355,11 @@ void Automation::MouseMove(const WebViewId& view_id,
   if (*error)
     return;
 
-  std::string error_msg;
+  automation::Error auto_error;
   if (!SendMouseMoveJSONRequest(
           automation(), view_locator, p.rounded_x(), p.rounded_y(),
-          &error_msg)) {
-    *error = new Error(kUnknownError, error_msg);
+          &auto_error)) {
+    *error = Error::FromAutomationError(auto_error);
   }
 }
 
@@ -372,11 +372,11 @@ void Automation::MouseClick(const WebViewId& view_id,
   if (*error)
     return;
 
-  std::string error_msg;
+  automation::Error auto_error;
   if (!SendMouseClickJSONRequest(
           automation(), view_locator, button, p.rounded_x(),
-          p.rounded_y(), &error_msg)) {
-    *error = new Error(kUnknownError, error_msg);
+          p.rounded_y(), &auto_error)) {
+    *error = Error::FromAutomationError(auto_error);
   }
 }
 
@@ -389,11 +389,11 @@ void Automation::MouseDrag(const WebViewId& view_id,
   if (*error)
     return;
 
-  std::string error_msg;
+  automation::Error auto_error;
   if (!SendMouseDragJSONRequest(
           automation(), view_locator, start.rounded_x(), start.rounded_y(),
-          end.rounded_x(), end.rounded_y(), &error_msg)) {
-    *error = new Error(kUnknownError, error_msg);
+          end.rounded_x(), end.rounded_y(), &auto_error)) {
+    *error = Error::FromAutomationError(auto_error);
   }
 }
 
@@ -409,11 +409,11 @@ void Automation::MouseButtonUp(const WebViewId& view_id,
   if (*error)
     return;
 
-  std::string error_msg;
+  automation::Error auto_error;
   if (!SendMouseButtonUpJSONRequest(
           automation(), view_locator, p.rounded_x(), p.rounded_y(),
-          &error_msg)) {
-    *error = new Error(kUnknownError, error_msg);
+          &auto_error)) {
+    *error = Error::FromAutomationError(auto_error);
   }
 }
 
@@ -429,11 +429,11 @@ void Automation::MouseButtonDown(const WebViewId& view_id,
   if (*error)
     return;
 
-  std::string error_msg;
+  automation::Error auto_error;
   if (!SendMouseButtonDownJSONRequest(
           automation(), view_locator, p.rounded_x(), p.rounded_y(),
-          &error_msg)) {
-    *error = new Error(kUnknownError, error_msg);
+          &auto_error)) {
+    *error = Error::FromAutomationError(auto_error);
   }
 }
 
@@ -449,11 +449,11 @@ void Automation::MouseDoubleClick(const WebViewId& view_id,
   if (*error)
     return;
 
-  std::string error_msg;
+  automation::Error auto_error;
   if (!SendMouseDoubleClickJSONRequest(
           automation(), view_locator, p.rounded_x(), p.rounded_y(),
-          &error_msg)) {
-    *error = new Error(kUnknownError, error_msg);
+          &auto_error)) {
+    *error = Error::FromAutomationError(auto_error);
   }
 }
 
@@ -466,11 +466,11 @@ void Automation::DragAndDropFilePaths(
     return;
   }
 
-  std::string error_msg;
+  automation::Error auto_error;
   if (!SendDragAndDropFilePathsJSONRequest(
           automation(), view_locator, location.rounded_x(),
-          location.rounded_y(), paths, &error_msg)) {
-    *error = new Error(kUnknownError, error_msg);
+          location.rounded_y(), paths, &auto_error)) {
+    *error = Error::FromAutomationError(auto_error);
   }
 }
 
@@ -482,10 +482,10 @@ void Automation::SendWebKeyEvent(const WebViewId& view_id,
   if (*error)
     return;
 
-  std::string error_msg;
+  automation::Error auto_error;
   if (!SendWebKeyEventJSONRequest(
-          automation(), view_locator, key_event, &error_msg)) {
-    *error = new Error(kUnknownError, error_msg);
+          automation(), view_locator, key_event, &auto_error)) {
+    *error = Error::FromAutomationError(auto_error);
   }
 }
 
@@ -498,10 +498,10 @@ void Automation::SendNativeKeyEvent(const WebViewId& view_id,
   if (*error)
     return;
 
-  std::string error_msg;
+  automation::Error auto_error;
   if (!SendNativeKeyEventJSONRequest(
-         automation(), view_locator, key_code, modifiers, &error_msg)) {
-    *error = new Error(kUnknownError, error_msg);
+         automation(), view_locator, key_code, modifiers, &auto_error)) {
+    *error = Error::FromAutomationError(auto_error);
   }
 }
 
@@ -513,10 +513,10 @@ void Automation::CaptureEntirePageAsPNG(const WebViewId& view_id,
   if (*error)
     return;
 
-  std::string error_msg;
+  automation::Error auto_error;
   if (!SendCaptureEntirePageJSONRequest(
-          automation(), view_locator, path, &error_msg)) {
-    *error = new Error(kUnknownError, error_msg);
+          automation(), view_locator, path, &auto_error)) {
+    *error = Error::FromAutomationError(auto_error);
   }
 }
 
@@ -529,11 +529,11 @@ void Automation::NavigateToURL(const WebViewId& view_id,
     return;
 
   AutomationMsg_NavigationResponseValues navigate_response;
-  std::string error_msg;
+  automation::Error auto_error;
   if (!SendNavigateToURLJSONRequest(automation(), view_locator,
                                     url, 1, &navigate_response,
-                                    &error_msg)) {
-    *error = new Error(kUnknownError, error_msg);
+                                    &auto_error)) {
+    *error = Error::FromAutomationError(auto_error);
     return;
   }
   // TODO(kkania): Do not rely on this enum.
@@ -549,12 +549,12 @@ void Automation::NavigateToURLAsync(const WebViewId& view_id,
   if (*error)
     return;
 
-  std::string error_msg;
+  automation::Error auto_error;
   if (!view_id.old_style()) {
     AutomationMsg_NavigationResponseValues navigate_response;
     if (!SendNavigateToURLJSONRequest(automation(), view_locator, url,
-                                      0, &navigate_response, &error_msg)) {
-      *error = new Error(kUnknownError, error_msg);
+                                      0, &navigate_response, &auto_error)) {
+      *error = Error::FromAutomationError(auto_error);
       return;
     }
   } else {
@@ -582,10 +582,10 @@ void Automation::GoForward(const WebViewId& view_id, Error** error) {
   if (*error)
     return;
 
-  std::string error_msg;
+  automation::Error auto_error;
   if (!SendGoForwardJSONRequest(
-          automation(), view_locator, &error_msg)) {
-    *error = new Error(kUnknownError, error_msg);
+          automation(), view_locator, &auto_error)) {
+    *error = Error::FromAutomationError(auto_error);
   }
 }
 
@@ -595,9 +595,9 @@ void Automation::GoBack(const WebViewId& view_id, Error** error) {
   if (*error)
     return;
 
-  std::string error_msg;
-  if (!SendGoBackJSONRequest(automation(), view_locator, &error_msg))
-    *error = new Error(kUnknownError, error_msg);
+  automation::Error auto_error;
+  if (!SendGoBackJSONRequest(automation(), view_locator, &auto_error))
+    *error = Error::FromAutomationError(auto_error);
 }
 
 void Automation::Reload(const WebViewId& view_id, Error** error) {
@@ -606,35 +606,35 @@ void Automation::Reload(const WebViewId& view_id, Error** error) {
   if (*error)
     return;
 
-  std::string error_msg;
-  if (!SendReloadJSONRequest(automation(), view_locator, &error_msg))
-    *error = new Error(kUnknownError, error_msg);
+  automation::Error auto_error;
+  if (!SendReloadJSONRequest(automation(), view_locator, &auto_error))
+    *error = Error::FromAutomationError(auto_error);
 }
 
 void Automation::GetCookies(const std::string& url,
                             ListValue** cookies,
                             Error** error) {
-  std::string error_msg;
-  if (!SendGetCookiesJSONRequest(automation(), url, cookies, &error_msg))
-    *error = new Error(kUnknownError, error_msg);
+  automation::Error auto_error;
+  if (!SendGetCookiesJSONRequest(automation(), url, cookies, &auto_error))
+    *error = Error::FromAutomationError(auto_error);
 }
 
 void Automation::DeleteCookie(const std::string& url,
                               const std::string& cookie_name,
                               Error** error) {
-  std::string error_msg;
+  automation::Error auto_error;
   if (!SendDeleteCookieJSONRequest(
-          automation(), url, cookie_name, &error_msg)) {
-    *error = new Error(kUnknownError, error_msg);
+          automation(), url, cookie_name, &auto_error)) {
+    *error = Error::FromAutomationError(auto_error);
   }
 }
 
 void Automation::SetCookie(const std::string& url,
                            DictionaryValue* cookie_dict,
                            Error** error) {
-  std::string error_msg;
-  if (!SendSetCookieJSONRequest(automation(), url, cookie_dict, &error_msg))
-    *error = new Error(kUnknownError, error_msg);
+  automation::Error auto_error;
+  if (!SendSetCookieJSONRequest(automation(), url, cookie_dict, &auto_error))
+    *error = Error::FromAutomationError(auto_error);
 }
 
 void Automation::GetViews(std::vector<WebViewInfo>* views,
@@ -644,27 +644,27 @@ void Automation::GetViews(std::vector<WebViewInfo>* views,
   if (*error)
     return;
 
-  std::string error_msg;
+  automation::Error auto_error;
   if (has_views) {
-    if (!SendGetWebViewsJSONRequest(automation(), views, &error_msg))
-      *error = new Error(kUnknownError, error_msg);
+    if (!SendGetWebViewsJSONRequest(automation(), views, &auto_error))
+      *error = Error::FromAutomationError(auto_error);
   } else {
-    if (!SendGetTabIdsJSONRequest(automation(), views, &error_msg))
-      *error = new Error(kUnknownError, error_msg);
+    if (!SendGetTabIdsJSONRequest(automation(), views, &auto_error))
+      *error = Error::FromAutomationError(auto_error);
   }
 }
 
 void Automation::DoesViewExist(
     const WebViewId& view_id, bool* does_exist, Error** error) {
-  std::string error_msg;
+  automation::Error auto_error;
   if (view_id.old_style()) {
     if (!SendIsTabIdValidJSONRequest(
-            automation(), view_id, does_exist, &error_msg))
-      *error = new Error(kUnknownError, error_msg);
+            automation(), view_id, does_exist, &auto_error))
+      *error = Error::FromAutomationError(auto_error);
   } else {
     if (!SendDoesAutomationObjectExistJSONRequest(
-            automation(), view_id, does_exist, &error_msg))
-      *error = new Error(kUnknownError, error_msg);
+            automation(), view_id, does_exist, &auto_error))
+      *error = Error::FromAutomationError(auto_error);
   }
 }
 
@@ -674,9 +674,9 @@ void Automation::CloseView(const WebViewId& view_id, Error** error) {
   if (*error)
     return;
 
-  std::string error_msg;
-  if (!SendCloseViewJSONRequest(automation(), view_locator, &error_msg))
-    *error = new Error(kUnknownError, error_msg);
+  automation::Error auto_error;
+  if (!SendCloseViewJSONRequest(automation(), view_locator, &auto_error))
+    *error = Error::FromAutomationError(auto_error);
 }
 
 void Automation::GetAppModalDialogMessage(std::string* message, Error** error) {
@@ -684,10 +684,10 @@ void Automation::GetAppModalDialogMessage(std::string* message, Error** error) {
   if (*error)
     return;
 
-  std::string error_msg;
+  automation::Error auto_error;
   if (!SendGetAppModalDialogMessageJSONRequest(
-          automation(), message, &error_msg)) {
-    *error = new Error(kUnknownError, error_msg);
+          automation(), message, &auto_error)) {
+    *error = Error::FromAutomationError(auto_error);
   }
 }
 
@@ -696,10 +696,10 @@ void Automation::AcceptOrDismissAppModalDialog(bool accept, Error** error) {
   if (*error)
     return;
 
-  std::string error_msg;
+  automation::Error auto_error;
   if (!SendAcceptOrDismissAppModalDialogJSONRequest(
-          automation(), accept, &error_msg)) {
-    *error = new Error(kUnknownError, error_msg);
+          automation(), accept, &auto_error)) {
+    *error = Error::FromAutomationError(auto_error);
   }
 }
 
@@ -709,10 +709,10 @@ void Automation::AcceptPromptAppModalDialog(const std::string& prompt_text,
   if (*error)
     return;
 
-  std::string error_msg;
+  automation::Error auto_error;
   if (!SendAcceptPromptAppModalDialogJSONRequest(
-          automation(), prompt_text, &error_msg)) {
-    *error = new Error(kUnknownError, error_msg);
+          automation(), prompt_text, &auto_error)) {
+    *error = Error::FromAutomationError(auto_error);
   }
 }
 
@@ -721,15 +721,15 @@ void Automation::GetBrowserVersion(std::string* version) {
 }
 
 void Automation::GetChromeDriverAutomationVersion(int* version, Error** error) {
-  std::string error_msg;
-  if (!SendGetChromeDriverAutomationVersion(automation(), version, &error_msg))
-    *error = new Error(kUnknownError, error_msg);
+  automation::Error auto_error;
+  if (!SendGetChromeDriverAutomationVersion(automation(), version, &auto_error))
+    *error = Error::FromAutomationError(auto_error);
 }
 
 void Automation::WaitForAllViewsToStopLoading(Error** error) {
-  std::string error_msg;
-  if (!SendWaitForAllViewsToStopLoadingJSONRequest(automation(), &error_msg))
-    *error = new Error(kUnknownError, error_msg);
+  automation::Error auto_error;
+  if (!SendWaitForAllViewsToStopLoadingJSONRequest(automation(), &auto_error))
+    *error = Error::FromAutomationError(auto_error);
 }
 
 void Automation::InstallExtensionDeprecated(
@@ -744,11 +744,11 @@ void Automation::InstallExtension(
   if (*error)
     return;
 
-  std::string error_msg;
+  automation::Error auto_error;
   if (!SendInstallExtensionJSONRequest(
           automation(), path, false /* with_ui */, extension_id,
-          &error_msg))
-    *error = new Error(kUnknownError, error_msg);
+          &auto_error))
+    *error = Error::FromAutomationError(auto_error);
 }
 
 void Automation::GetExtensionsInfo(
@@ -757,10 +757,10 @@ void Automation::GetExtensionsInfo(
   if (*error)
     return;
 
-  std::string error_msg;
+  automation::Error auto_error;
   if (!SendGetExtensionsInfoJSONRequest(
-          automation(), extensions_list, &error_msg))
-    *error = new Error(kUnknownError, error_msg);
+          automation(), extensions_list, &auto_error))
+    *error = Error::FromAutomationError(auto_error);
 }
 
 void Automation::IsPageActionVisible(
@@ -772,10 +772,10 @@ void Automation::IsPageActionVisible(
   if (*error)
     return;
 
-  std::string error_msg;
+  automation::Error auto_error;
   if (!SendIsPageActionVisibleJSONRequest(
-          automation(), tab_id, extension_id, is_visible, &error_msg))
-    *error = new Error(kUnknownError, error_msg);
+          automation(), tab_id, extension_id, is_visible, &auto_error))
+    *error = Error::FromAutomationError(auto_error);
 }
 
 void Automation::SetExtensionState(
@@ -786,21 +786,21 @@ void Automation::SetExtensionState(
   if (*error)
     return;
 
-  std::string error_msg;
+  automation::Error auto_error;
   if (!SendSetExtensionStateJSONRequest(
           automation(), extension_id, enable /* enable */,
-          false /* allow_in_incognito */, &error_msg))
-    *error = new Error(kUnknownError, error_msg);
+          false /* allow_in_incognito */, &auto_error))
+    *error = Error::FromAutomationError(auto_error);
 }
 
 void Automation::ClickExtensionButton(
     const std::string& extension_id,
     bool browser_action,
     Error** error) {
-  std::string error_msg;
+  automation::Error auto_error;
   if (!SendClickExtensionButtonJSONRequest(
-          automation(), extension_id, browser_action, &error_msg))
-    *error = new Error(kUnknownError, error_msg);
+          automation(), extension_id, browser_action, &auto_error))
+    *error = Error::FromAutomationError(auto_error);
 }
 
 void Automation::UninstallExtension(
@@ -809,10 +809,10 @@ void Automation::UninstallExtension(
   if (*error)
     return;
 
-  std::string error_msg;
+  automation::Error auto_error;
   if (!SendUninstallExtensionJSONRequest(
-          automation(), extension_id, &error_msg))
-    *error = new Error(kUnknownError, error_msg);
+          automation(), extension_id, &auto_error))
+    *error = Error::FromAutomationError(auto_error);
 }
 
 void Automation::SetLocalStatePreference(const std::string& pref,
@@ -827,10 +827,10 @@ void Automation::SetLocalStatePreference(const std::string& pref,
     return;
 
   if (has_new_local_state_api) {
-    std::string error_msg;
+    automation::Error auto_error;
     if (!SendSetLocalStatePreferenceJSONRequest(
-            automation(), pref, scoped_value.release(), &error_msg))
-      *error = new Error(kUnknownError, error_msg);
+            automation(), pref, scoped_value.release(), &auto_error))
+      *error = Error::FromAutomationError(auto_error);
   } else {
     std::string request, response;
     DictionaryValue request_dict;
@@ -858,10 +858,10 @@ void Automation::SetPreference(const std::string& pref,
     return;
 
   if (has_new_pref_api) {
-    std::string error_msg;
+    automation::Error auto_error;
     if (!SendSetPreferenceJSONRequest(
-            automation(), pref, scoped_value.release(), &error_msg))
-      *error = new Error(kUnknownError, error_msg);
+            automation(), pref, scoped_value.release(), &auto_error))
+      *error = Error::FromAutomationError(auto_error);
   } else {
     std::string request, response;
     DictionaryValue request_dict;
@@ -886,11 +886,11 @@ Error* Automation::ConvertViewIdToLocator(
     const WebViewId& view_id, WebViewLocator* view_locator) {
   if (view_id.old_style()) {
     int browser_index, tab_index;
-    std::string error_msg;
+    automation::Error auto_error;
     if (!SendGetIndicesFromTabIdJSONRequest(
             automation(), view_id.tab_id(), &browser_index, &tab_index,
-            &error_msg))
-      return new Error(kUnknownError, error_msg);
+            &auto_error))
+      return Error::FromAutomationError(auto_error);
     *view_locator = WebViewLocator::ForIndexPair(browser_index, tab_index);
   } else {
     *view_locator = WebViewLocator::ForViewId(view_id.GetId());
diff --git a/chrome/test/webdriver/webdriver_error.cc b/chrome/test/webdriver/webdriver_error.cc
index 200d797..0884e10 100644
--- a/chrome/test/webdriver/webdriver_error.cc
+++ b/chrome/test/webdriver/webdriver_error.cc
@@ -6,6 +6,8 @@
 
 #include <sstream>
 
+#include "chrome/common/automation_constants.h"
+
 namespace webdriver {
 
 namespace {
@@ -39,6 +41,10 @@ const char* DefaultMessageForErrorCode(ErrorCode code) {
       return "The cookie domain is invalid";
     case kUnableToSetCookie:
       return "Unable to set cookie";
+    case kUnexpectedAlertOpen:
+      return "An open modal dialog blocked the operation";
+    case kNoAlertOpenError:
+      return "No JavaScript modal dialog is open";
     default:
       return "<unknown>";
   }
@@ -46,6 +52,46 @@ const char* DefaultMessageForErrorCode(ErrorCode code) {
 
 }  // namespace
 
+// static
+Error* Error::FromAutomationError(const automation::Error& error) {
+  ErrorCode code = kUnknownError;
+  switch (error.code()) {
+    case automation::kNoJavaScriptModalDialogOpen:
+      code = kNoAlertOpenError;
+      break;
+    case automation::kBlockedByModalDialog:
+      code = kUnexpectedAlertOpen;
+      break;
+    default:
+      break;
+  }
+
+  // In Chrome 17 and before, the automation error was just a string.
+  // Compare against some strings that correspond to webdriver errors.
+  // TODO(kkania): Remove these comparisons when Chrome 17 is unsupported.
+  if (code == kUnknownError) {
+    if (error.message() ==
+            "Command cannot be performed because a modal dialog is active" ||
+        error.message() ==
+            "Could not complete script execution because a modal "
+                "dialog is active") {
+      code = kUnexpectedAlertOpen;
+    } else if (error.message() == "No modal dialog is showing" ||
+               error.message() == "No JavaScript modal dialog is showing") {
+      code = kNoAlertOpenError;
+    }
+  }
+
+  // If the automation error code did not refer to a webdriver error code
+  // (besides unknown), include the error message from chrome. Otherwise,
+  // include the webdriver error code and the webdriver error message.
+  if (code == kUnknownError) {
+    return new Error(code, error.message());
+  } else {
+    return new Error(code);
+  }
+}
+
 Error::Error(ErrorCode code)
     : code_(code),
       details_(DefaultMessageForErrorCode(code)) {
diff --git a/chrome/test/webdriver/webdriver_error.h b/chrome/test/webdriver/webdriver_error.h
index 0ed0c51..dbc7229d 100644
--- a/chrome/test/webdriver/webdriver_error.h
+++ b/chrome/test/webdriver/webdriver_error.h
@@ -10,6 +10,10 @@
 
 #include "base/basictypes.h"
 
+namespace automation {
+class Error;
+}
+
 namespace webdriver {
 
 // Error codes defined by the WebDriver wire protcol.
@@ -28,6 +32,8 @@ enum ErrorCode {
   kNoSuchWindow = 23,
   kInvalidCookieDomain = 24,
   kUnableToSetCookie = 25,
+  kUnexpectedAlertOpen = 26,
+  kNoAlertOpenError = 27,
 
   // HTTP status codes.
   kSeeOther = 303,
@@ -40,6 +46,8 @@ enum ErrorCode {
 // Represents a WebDriver error and the context within which the error occurred.
 class Error {
  public:
+  static Error* FromAutomationError(const automation::Error& error);
+
   explicit Error(ErrorCode code);
 
   Error(ErrorCode code, const std::string& details);
diff --git a/chrome/test/webdriver/webdriver_session.cc b/chrome/test/webdriver/webdriver_session.cc
index e1a25c6..c5b1c16 100644
--- a/chrome/test/webdriver/webdriver_session.cc
+++ b/chrome/test/webdriver/webdriver_session.cc
@@ -921,12 +921,22 @@ Error* Session::IsOptionElementSelected(const FrameId& frame_id,
 Error* Session::SetOptionElementSelected(const FrameId& frame_id,
                                          const ElementId& element,
                                          bool selected) {
-  return ExecuteScriptAndParse(
+  // This wrapper ensures the script is started successfully and
+  // allows for an alert to happen when the option selection occurs.
+  // See selenium bug 2671.
+  const char kSetSelectedWrapper[] =
+      "var args = [].slice.apply(arguments);"
+      "args[args.length - 1]();"
+      "return (%s).apply(null, args.slice(0, args.length - 1));";
+  Value* value = NULL;
+  Error* error = ExecuteAsyncScript(
       frame_id,
-      atoms::asString(atoms::SET_SELECTED),
-      "setSelected",
+      base::StringPrintf(kSetSelectedWrapper,
+                         atoms::asString(atoms::SET_SELECTED).c_str()),
       CreateListValueFrom(element, selected),
-      CreateDirectValueParser(kSkipParsing));
+      &value);
+  scoped_ptr<Value> scoped_value(value);
+  return error;
 }
 
 Error* Session::ToggleOptionElement(const FrameId& frame_id,