Upgrade Wasm JS API, step 1

src/wasm/wasm-result.cc

Index: src/wasm/wasm-result.cc
diff --git a/src/wasm/wasm-result.cc b/src/wasm/wasm-result.cc
index 0f5529fe385fc1a427930b6a562c1c73ede46ba4..30268ac8ad52d4ee03ee3b80e99393283e77d2f7 100644
--- a/src/wasm/wasm-result.cc
+++ b/src/wasm/wasm-result.cc
@@ -28,11 +28,10 @@ std::ostream& operator<<(std::ostream& os, const ErrorCode& error_code) {
 }
 
 void ErrorThrower::Error(const char* format, ...) {
-  // only report the first error.
-  if (error_ || isolate_->has_pending_exception()) return;
-  error_ = true;
-  char buffer[256];
+  // 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);
@@ -44,8 +43,13 @@ void ErrorThrower::Error(const char* format, ...) {
   }
   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