ChromeDriver should be able to focus on a frame using its frame element,

chrome/test/webdriver/commands/webelement_commands.cc

 // Copyright (c) 2010 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 "chrome/test/webdriver/commands/webelement_commands.h"
 
 #include "base/scoped_ptr.h"
 #include "base/stringprintf.h"
 #include "base/third_party/icu/icu_utf.h"
 #include "base/values.h"
@@ skipping 201 matching lines @@
   if (path_segments_.size() < 7) {
     SET_WEBDRIVER_ERROR(response, "Path segments is less than 7",
                         kBadRequest);
     return;
   }
 
   std::string script = "return arguments[0] == arguments[1];";
 
   scoped_ptr<ListValue> args(new ListValue);
   args->Append(element.ToValue());
-  args->Append(Value::CreateStringValue(path_segments_.at(6)));
+
+  WebElementId other_element(path_segments_.at(6));
+  args->Append(other_element.ToValue());
 
   Value* result = NULL;
   ErrorCode status = session_->ExecuteScript(script, args.get(), &result);
   response->SetStatus(status);
   response->SetValue(result);
 }
 
 ///////////////////// ElementLocationCommand ////////////////////
 
 ElementLocationCommand::ElementLocationCommand(
@@ skipping 301 matching lines @@
     SET_WEBDRIVER_ERROR(response,
                         "Result is not string type",
                         kInternalServerError);
     return;
   }
   response->SetStatus(kSuccess);
   response->SetValue(result.release());
 }
 
 }  // namespace webdriver