[wasm] W.validate should not throw on failure

R=titzer@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2640113005
Cr-Commit-Position: refs/heads/master@{#42556}

src/wasm/wasm-js.cc

@@ -159,6 +159,7 @@ void WebAssemblyValidate(const v8::FunctionCallbackInfo<v8::Value>& args) {
   if (ValidateModule(isolate, args[0], &thrower)) {
     return_value.Set(v8::True(isolate));
   } else {
+    if (thrower.wasm_error()) thrower.Reify();  // Clear error.
     return_value.Set(v8::False(isolate));
   }
 }

src/wasm/wasm-result.cc

@@ -64,6 +64,7 @@ void ErrorThrower::RangeError(const char* format, ...) {
 
 void ErrorThrower::CompileError(const char* format, ...) {
   if (error()) return;
+  wasm_error_ = true;
   va_list arguments;
   va_start(arguments, format);
   Format(isolate_->wasm_compile_error_function(), format, arguments);
@@ -72,6 +73,7 @@ void ErrorThrower::CompileError(const char* format, ...) {
 
 void ErrorThrower::LinkError(const char* format, ...) {
   if (error()) return;
+  wasm_error_ = true;
   va_list arguments;
   va_start(arguments, format);
   Format(isolate_->wasm_link_error_function(), format, arguments);
@@ -80,6 +82,7 @@ void ErrorThrower::LinkError(const char* format, ...) {
 
 void ErrorThrower::RuntimeError(const char* format, ...) {
   if (error()) return;
+  wasm_error_ = true;
   va_list arguments;
   va_start(arguments, format);
   Format(isolate_->wasm_runtime_error_function(), format, arguments);

src/wasm/wasm-result.h

@@ -112,6 +112,7 @@ class V8_EXPORT_PRIVATE ErrorThrower {
   }
 
   bool error() const { return !exception_.is_null(); }
+  bool wasm_error() { return wasm_error_; }
 
  private:
   void Format(i::Handle<i::JSFunction> constructor, const char* fmt, va_list);
@@ -119,6 +120,7 @@ class V8_EXPORT_PRIVATE ErrorThrower {
   i::Isolate* isolate_;
   const char* context_;
   i::Handle<i::Object> exception_;
+  bool wasm_error_ = false;
 };
 }  // namespace wasm
 }  // namespace internal