Make String::Empty inlineable.

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index 7b94a59a29f806ede93ec2b174a5a54825d7016e..90245319928d068756e92b3106ee9961e123031b 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -1084,6 +1084,7 @@ class String : public Primitive {
    * A zero length string.
    */
   V8EXPORT static v8::Local<v8::String> Empty();
+  inline static v8::Local<v8::String> Empty(Isolate* isolate);
 
   /**
    * Returns true if the string is external
@@ -3903,6 +3904,7 @@ class Internals {
   static const int kNullValueRootIndex = 7;
   static const int kTrueValueRootIndex = 8;
   static const int kFalseValueRootIndex = 9;
+  static const int kEmptySymbolRootIndex = 128;
 
   static const int kJSObjectType = 0xaa;
   static const int kFirstNonstringType = 0x80;
@@ -4221,6 +4223,15 @@ String* String::Cast(v8::Value* value) {
 }
 
 
+Local<String> String::Empty(Isolate* isolate) {
+  typedef internal::Object* S;
+  typedef internal::Internals I;
+  if (!I::IsInitialized(isolate)) return Empty();
+  S* slot = I::GetRoot(isolate, I::kEmptySymbolRootIndex);
+  return Local<String>(reinterpret_cast<String*>(slot));
+}
+
+
 String::ExternalStringResource* String::GetExternalStringResource() const {
   typedef internal::Object O;
   typedef internal::Internals I;