Upgrade Wasm JS API, step 1

src/wasm/wasm-result.h

 // 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.
 
 #ifndef V8_WASM_RESULT_H_
 #define V8_WASM_RESULT_H_
 
 #include "src/base/compiler-specific.h"
 #include "src/base/smart-pointers.h"
 
+#include "src/handles.h"
 #include "src/globals.h"
 
 namespace v8 {
 namespace internal {
 
 class Isolate;
 
 namespace wasm {
 
 // Error codes for programmatic checking of the decoder's verification.
@@ skipping 63 matching lines @@
   os << std::endl;
   return os;
 }
 
 std::ostream& operator<<(std::ostream& os, const ErrorCode& error_code);
 
 // A helper for generating error messages that bubble up to JS exceptions.
 class ErrorThrower {
  public:
   ErrorThrower(Isolate* isolate, const char* context)
-      : isolate_(isolate), context_(context), error_(false) {}
+      : isolate_(isolate), context_(context) {}
+  ~ErrorThrower();
 
   PRINTF_FORMAT(2, 3) void Error(const char* fmt, ...);
 
   template <typename T>
   void Failed(const char* error, Result<T>& result) {
     std::ostringstream str;
     str << error << result;
     return Error("%s", str.str().c_str());
   }
 
-  bool error() const { return error_; }
+  i::Handle<i::String> Reify() {
+    auto result = message_;
+    message_ = i::Handle<i::String>();
+    return result;
+  }
+
+  bool error() const { return !message_.is_null(); }
 
  private:
   Isolate* isolate_;
   const char* context_;
-  bool error_;
+  i::Handle<i::String> message_;
 };
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8
 
 #endif