Adds a --help option and usage message listing all flags to V8.

src/d8.cc

 // Copyright 2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 300 matching lines @@
     Handle<String> name = String::New("(d8)");
     ExecuteString(String::New(*input), name, true, true);
   }
   editor->Close();
   printf("\n");
 }
 
 
 int Shell::Main(int argc, char* argv[]) {
   i::FlagList::SetFlagsFromCommandLine(&argc, argv, true);
+  if (i::FLAG_help) {
+    return 1;
+  }
   Initialize();
   bool run_shell = (argc == 1);
   Context::Scope context_scope(evaluation_context_);
   for (int i = 1; i < argc; i++) {
     char* str = argv[i];
     HandleScope handle_scope;
     Handle<String> file_name = v8::String::New(str);
     Handle<String> source = ReadFile(str);
     if (source.IsEmpty()) {
       printf("Error reading '%s'\n", str);
       return 1;
     }
     if (!ExecuteString(source, file_name, false, true))
       return 1;
   }
   if (run_shell)
     RunShell();
   OnExit();
   return 0;
 }
 
 
 }  // namespace v8
 
 
 int main(int argc, char* argv[]) {
   return v8::Shell::Main(argc, argv);
 }