Return MaybeHandle from NewExternalStringFrom*.

test/cctest/test-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 15104 matching lines @@
     LocalContext env;
     i::Factory* factory = CcTest::i_isolate()->factory();
     v8::HandleScope scope(env->GetIsolate());
     AsciiVectorResource ascii_resource(
         i::Vector<const char>(c_string, i::StrLength(c_string)));
     UC16VectorResource uc16_resource(
         i::Vector<const uint16_t>(two_byte_string,
                                   i::StrLength(c_string)));
 
     Local<String> lhs(v8::Utils::ToLocal(
-        factory->NewExternalStringFromAscii(&ascii_resource)));
+        factory->NewExternalStringFromAscii(&ascii_resource)
+            .ToHandleChecked()));
     Local<String> rhs(v8::Utils::ToLocal(
-        factory->NewExternalStringFromAscii(&ascii_resource)));
+        factory->NewExternalStringFromAscii(&ascii_resource)
+            .ToHandleChecked()));
 
     env->Global()->Set(v8_str("lhs"), lhs);
     env->Global()->Set(v8_str("rhs"), rhs);
 
     CompileRun(
         "var cons = lhs + rhs;"
         "var slice = lhs.substring(1, lhs.length - 1);"
         "var slice_on_cons = (lhs + rhs).substring(1, lhs.length *2 - 1);");
 
     CHECK(lhs->IsOneByte());
@@ skipping 7277 matching lines @@
              "f.call(friend);");
   CHECK_EQ(2, named_access_count);
 
   // Test access using Object.setPrototypeOf reflective method.
   named_access_count = 0;
   CompileRun("Object.setPrototypeOf(friend, {});");
   CHECK_EQ(1, named_access_count);
   CompileRun("Object.getPrototypeOf(friend);");
   CHECK_EQ(2, named_access_count);
 }