Make sure the fatal OOM handler never returns.

src/api.cc

 // Copyright 2012 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 207 matching lines @@
   if (isolate->heap()->HasBeenSetUp()) {
     // BUG(1718): Don't use the take_snapshot since we don't support
     // HeapIterator here without doing a special GC.
     isolate->heap()->RecordStats(&heap_stats, false);
   }
   isolate->SignalFatalError();
   FatalErrorCallback callback = GetFatalErrorHandler();
   const char* message = "Allocation failed - process out of memory";
   callback(location, message);
   // If the callback returns, we stop execution.
-  UNREACHABLE();
+  FATAL("API fatal error handler returned after process out of memory");
 }
 
 
 bool Utils::ReportApiFailure(const char* location, const char* message) {
   FatalErrorCallback callback = GetFatalErrorHandler();
   callback(location, message);
   i::Isolate* isolate = i::Isolate::Current();
   isolate->SignalFatalError();
   return false;
 }
@@ skipping 7627 matching lines @@
   Isolate* isolate = reinterpret_cast<Isolate*>(info.GetIsolate());
   Address callback_address =
       reinterpret_cast<Address>(reinterpret_cast<intptr_t>(callback));
   VMState<EXTERNAL> state(isolate);
   ExternalCallbackScope call_scope(isolate, callback_address);
   return callback(info);
 }
 
 
 } }  // namespace v8::internal