Upgrade Wasm JS API, step 1

src/wasm/wasm-result.cc

 // Copyright 2015 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 "src/wasm/wasm-result.h"
 
 #include "src/factory.h"
 #include "src/heap/heap.h"
 #include "src/isolate-inl.h"
 #include "src/objects.h"
@@ skipping 10 matching lines @@
       os << "Success";
       break;
     default:  // TODO(titzer): render error codes
       os << "Error";
       break;
   }
   return os;
 }
 
 void ErrorThrower::Error(const char* format, ...) {
-  // only report the first error.
-  if (error_ || isolate_->has_pending_exception()) return;
-  error_ = true;
+  // Only report the first error.
+  if (error()) return;
+
   char buffer[256];
-
   va_list arguments;
   va_start(arguments, format);
   base::OS::VSNPrintF(buffer, 255, format, arguments);
   va_end(arguments);
 
   std::ostringstream str;
   if (context_ != nullptr) {
     str << context_ << ": ";
   }
   str << buffer;
 
-  isolate_->ScheduleThrow(
-      *isolate_->factory()->NewStringFromAsciiChecked(str.str().c_str()));
+  message_ = isolate_->factory()->NewStringFromAsciiChecked(str.str().c_str());
+}
+
+ErrorThrower::~ErrorThrower() {
+  if (error() && !isolate_->has_pending_exception()) {
+    isolate_->ScheduleThrow(*message_);
+  }
 }
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8