Tweak the TurboFan pipeline for stub compilation.

src/runtime/runtime-strings.cc

 // Copyright 2014 the V8 project 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 "src/v8.h"
 
 #include "src/arguments.h"
 #include "src/jsregexp-inl.h"
 #include "src/jsregexp.h"
 #include "src/runtime/runtime-utils.h"
@@ skipping 1283 matching lines @@
   if (!args[1]->IsNumber()) return isolate->heap()->undefined_value();
   if (std::isinf(args.number_at(1))) return isolate->heap()->nan_value();
   return __RT_impl_Runtime_StringCharCodeAtRT(args, isolate);
 }
 
 
 RUNTIME_FUNCTION(Runtime_IsStringWrapperSafeForDefaultValueOf) {
   UNIMPLEMENTED();
   return NULL;
 }
+
+
+RUNTIME_FUNCTION(Runtime_StringGetLength) {
+  HandleScope scope(isolate);
+  DCHECK(args.length() == 1);
+  CONVERT_ARG_HANDLE_CHECKED(String, s, 0);
+  return Smi::FromInt(s->length());
+}
 }
 }  // namespace v8::internal