Return MaybeHandle from NewExternalStringFrom*.

test/cctest/test-parsing.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 637 matching lines @@
   i::HandleScope test_scope(isolate);
   i::SmartArrayPointer<i::uc16> uc16_buffer(new i::uc16[length]);
   for (unsigned i = 0; i < length; i++) {
     uc16_buffer[i] = static_cast<i::uc16>(ascii_source[i]);
   }
   i::Vector<const char> ascii_vector(ascii_source, static_cast<int>(length));
   i::Handle<i::String> ascii_string(
       factory->NewStringFromAscii(ascii_vector));
   TestExternalResource resource(uc16_buffer.get(), length);
   i::Handle<i::String> uc16_string(
-      factory->NewExternalStringFromTwoByte(&resource));
+      factory->NewExternalStringFromTwoByte(&resource).ToHandleChecked());
 
   i::ExternalTwoByteStringUtf16CharacterStream uc16_stream(
       i::Handle<i::ExternalTwoByteString>::cast(uc16_string), start, end);
   i::GenericStringUtf16CharacterStream string_stream(ascii_string, start, end);
   i::Utf8ToUtf16CharacterStream utf8_stream(
       reinterpret_cast<const i::byte*>(ascii_source), end);
   utf8_stream.SeekForward(start);
 
   unsigned i = start;
   while (i < end) {
@@ skipping 1928 matching lines @@
   RunParserSyncTest(assignment_context_data, bad_statement_data_common, kError);
   RunParserSyncTest(assignment_context_data, bad_statement_data_for_assignment,
                     kError);
 
   RunParserSyncTest(prefix_context_data, good_statement_data, kSuccess);
   RunParserSyncTest(prefix_context_data, bad_statement_data_common, kError);
 
   RunParserSyncTest(postfix_context_data, good_statement_data, kSuccess);
   RunParserSyncTest(postfix_context_data, bad_statement_data_common, kError);
 }