Revert "Remove IsInitialized checks from inlined API functions."

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index de48424148b27c77959b058c1a56f22e7c84a319..4b5c5a9949779ee17770adbb8c8998ffcae13b8d 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -2893,16 +2893,6 @@ Local<Integer> Value::ToInteger() const {
 }
 
 
-#ifdef V8_ENABLE_CHECKS
-void i::Internals::CheckInitialized(v8::Isolate* external_isolate) {
-  i::Isolate* isolate = reinterpret_cast<i::Isolate*>(external_isolate);
-  ApiCheck(isolate != NULL && isolate->IsInitialized() && !i::V8::IsDead(),
-           "v8::internal::Internals::CheckInitialized()",
-           "Isolate is not initialized or V8 has died");
-}
-#endif
-
-
 void External::CheckCast(v8::Value* that) {
   if (IsDeadCheck(i::Isolate::Current(), "v8::External::Cast()")) return;
   ApiCheck(Utils::OpenHandle(that)->IsExternal(),