The command handler for /session/:sessionId/execute (execute_script) was...

chrome/test/webdriver/commands/execute_command.h

Index: chrome/test/webdriver/commands/execute_command.h
===================================================================
--- chrome/test/webdriver/commands/execute_command.h	(revision 75288)
+++ chrome/test/webdriver/commands/execute_command.h	(working copy)
@@ -10,6 +10,8 @@
 
 #include "chrome/test/webdriver/commands/webdriver_command.h"
 
+class ListValue;
+
 namespace webdriver {
 
 // Inject a snippet of javascript into the page and return its result.
@@ -33,8 +35,7 @@
   virtual bool RequiresValidTab();
 
   std::string script_;
-  bool has_args_;
-  std::string args_;
+  ListValue* args_;  // Value is owned by |Command::parameters_|.
 
   DISALLOW_COPY_AND_ASSIGN(ExecuteCommand);
 };