Upgrade Wasm JS API, step 1

src/wasm/wasm-result.h

Index: src/wasm/wasm-result.h
diff --git a/src/wasm/wasm-result.h b/src/wasm/wasm-result.h
index 9aa061de862b2f1f60a4507a38c0c127a51bc52b..e741de8e5e187e8a4fef4053f910128f61235e73 100644
--- a/src/wasm/wasm-result.h
+++ b/src/wasm/wasm-result.h
@@ -8,6 +8,7 @@
 #include "src/base/compiler-specific.h"
 #include "src/base/smart-pointers.h"
 
+#include "src/handles.h"
 #include "src/globals.h"
 
 namespace v8 {
@@ -91,7 +92,8 @@ std::ostream& operator<<(std::ostream& os, const ErrorCode& error_code);
 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, ...);
 
@@ -102,12 +104,18 @@ class ErrorThrower {
     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