bindings: Throw a type error if converting an interface or callback function fails.

third_party/WebKit/Source/bindings/templates/callback_function.cpp.tmpl

Index: third_party/WebKit/Source/bindings/templates/callback_function.cpp.tmpl
diff --git a/third_party/WebKit/Source/bindings/templates/callback_function.cpp.tmpl b/third_party/WebKit/Source/bindings/templates/callback_function.cpp.tmpl
index 50e3b25f6728ce7f06c67f4a1120ba8640239e42..6a0634e9ffd76817dd6cac165fd599ad8ea5cd0d 100644
--- a/third_party/WebKit/Source/bindings/templates/callback_function.cpp.tmpl
+++ b/third_party/WebKit/Source/bindings/templates/callback_function.cpp.tmpl
@@ -81,7 +81,10 @@ bool {{cpp_class}}::call({{argument_declarations | join(', ')}}) {
 }
 
 {{cpp_class}}* NativeValueTraits<{{cpp_class}}>::nativeValue(v8::Isolate* isolate, v8::Local<v8::Value> value, ExceptionState& exceptionState) {
-  return {{cpp_class}}::create(ScriptState::current(isolate), value);
+  {{cpp_class}}* nativeValue = {{cpp_class}}::create(ScriptState::current(isolate), value);
+  if (!nativeValue)
+    exceptionState.throwTypeError("Unable to convert value to {{cpp_class}}.");

[Yuki, 2017/04/07 13:37:21]

nit: Can we use {{idl_type}} instead?
I'm not 100% sure if {{idl_type}} is appropriate, but my point is that we should
use an IDL name rather than an internal C++ class' name because this is a
user-visible message.

+  return nativeValue;
 }
 
 }  // namespace blink