Do not eagerly convert exception to string when creating a message object

src/isolate.cc

 // Copyright 2012 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.
 
 #include <stdlib.h>
 
 #include <fstream>  // NOLINT(readability/streams)
 #include <sstream>
 
 #include "src/v8.h"
@@ skipping 1359 matching lines @@
     if (!ComputeLocationFromException(&potential_computed_location,
                                       exception)) {
       if (!ComputeLocationFromStackTrace(&potential_computed_location,
                                          exception)) {
         ComputeLocation(&potential_computed_location);
       }
     }
     location = &potential_computed_location;
   }
 
-  // If the exception argument is a custom object, turn it into a string
-  // before throwing as uncaught exception.  Note that the pending
-  // exception object to be set later must not be turned into a string.
-  if (exception->IsJSObject() && !IsErrorObject(exception)) {
-    MaybeHandle<Object> maybe_exception =
-        Execution::ToDetailString(this, exception);
-    if (!maybe_exception.ToHandle(&exception)) {
-      exception =
-          factory()->InternalizeOneByteString(STATIC_CHAR_VECTOR("exception"));
-    }
-  }
   return MessageHandler::MakeMessageObject(
       this, MessageTemplate::kUncaughtException, location, exception,
       stack_trace_object);
 }
 
 
 bool Isolate::IsJavaScriptHandlerOnTop(Object* exception) {
   DCHECK_NE(heap()->the_hole_value(), exception);
 
   // For uncatchable exceptions, the JavaScript handler cannot be on top.
@@ skipping 1384 matching lines @@
   if (prev_ && prev_->Intercept(flag)) return true;
   // Then check whether this scope intercepts.
   if ((flag & intercept_mask_)) {
     intercepted_flags_ |= flag;
     return true;
   }
   return false;
 }
 
 } }  // namespace v8::internal