Return MaybeHandle from NewExternalStringFrom*.

src/factory.h

 // 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.
 
 #ifndef V8_FACTORY_H_
 #define V8_FACTORY_H_
 
 #include "isolate.h"
 
 namespace v8 {
@@ skipping 148 matching lines @@
     if (begin == 0 && end == str->length()) return str;
     return NewProperSubString(str, begin, end);
   }
 
   Handle<SlicedString> NewRawSlicedString(String::Encoding encoding);
 
   // Creates a new external String object.  There are two String encodings
   // in the system: ASCII and two byte.  Unlike other String types, it does
   // not make sense to have a UTF-8 factory function for external strings,
   // because we cannot change the underlying buffer.
-  Handle<String> NewExternalStringFromAscii(
+  MaybeHandle<String> NewExternalStringFromAscii(
       const ExternalAsciiString::Resource* resource);
-  Handle<String> NewExternalStringFromTwoByte(
+  MaybeHandle<String> NewExternalStringFromTwoByte(
       const ExternalTwoByteString::Resource* resource);
 
   // Create a symbol.
   Handle<Symbol> NewSymbol();
   Handle<Symbol> NewPrivateSymbol();
 
   // Create a global (but otherwise uninitialized) context.
   Handle<Context> NewNativeContext();
 
   // Create a global context.
@@ skipping 407 matching lines @@
 
   // Update the map cache in the native context with (keys, map)
   Handle<MapCache> AddToMapCache(Handle<Context> context,
                                  Handle<FixedArray> keys,
                                  Handle<Map> map);
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_FACTORY_H_