Increase the chance of printing a useful error when bootstrapping fails

Two changes:
  - In ReportBootstrappingException, if all we have is a string, it seems
    better to print that than nothing.
  - In Factory::NewError, there's no use trying to call into the builtins if
    compilation of the builtins is causing the exception (this currently
    results in a cryptic segfault if we trigger, say, a ReferenceError when
    executing builtins script during bootstrapping).

Review URL: https://codereview.chromium.org/1158013003

Cr-Commit-Position: refs/heads/master@{#28912}

src/factory.cc

@@ -1061,6 +1061,13 @@ Handle<Object> Factory::NewError(const char* maker,
                                  Handle<Object> arg2) {
   HandleScope scope(isolate());
   Handle<String> error_maker = InternalizeUtf8String(maker);
+  if (isolate()->bootstrapper()->IsActive()) {
+    // If this exception is being thrown during bootstrapping,
+    // js_builtins_object is unavailable. We return the error maker
+    // name's string as the exception since we have nothing better
+    // to do.
+    return scope.CloseAndEscape(error_maker);
+  }
   Handle<Object> fun_obj = Object::GetProperty(isolate()->js_builtins_object(),
                                                error_maker).ToHandleChecked();
 

src/isolate.cc

@@ -937,6 +937,9 @@ void ReportBootstrappingException(Handle<Object> exception,
         "Extension or internal compilation error in %s at line %d.\n",
         String::cast(location->script()->name())->ToCString().get(),
         line_number);
+  } else if (exception->IsString()) {
+    base::OS::PrintError("Extension or internal compilation error: %s.\n",
+                         String::cast(*exception)->ToCString().get());
   } else {
     base::OS::PrintError("Extension or internal compilation error.\n");
   }

src/pending-compilation-error-handler.cc

@@ -41,6 +41,11 @@ void PendingCompilationErrorHandler::ThrowPendingError(Isolate* isolate,
       break;
   }
 
+  if (!error->IsJSObject()) {
+    isolate->Throw(*error, &location);
+    return;
+  }
+
   Handle<JSObject> jserror = Handle<JSObject>::cast(error);
 
   Handle<Name> key_start_pos = factory->error_start_pos_symbol();