API functions returning Promises should not throw exceptions.

Source/bindings/scripts/v8_types.py

Index: Source/bindings/scripts/v8_types.py
diff --git a/Source/bindings/scripts/v8_types.py b/Source/bindings/scripts/v8_types.py
index c2ebdcd17f1ec7428f7727a8f514f7d577c96930..ba5b67bbf56846ab976556c5884aa09f64770f01 100644
--- a/Source/bindings/scripts/v8_types.py
+++ b/Source/bindings/scripts/v8_types.py
@@ -523,7 +523,7 @@ def v8_value_to_cpp_value_array_or_sequence(native_array_element_type, v8_value,
     return expression
 
 
-def v8_value_to_local_cpp_value(idl_type, extended_attributes, v8_value, variable_name, index=None, declare_variable=True, isolate='info.GetIsolate()', used_in_private_script=False):
+def v8_value_to_local_cpp_value(idl_type, extended_attributes, v8_value, variable_name, index=None, declare_variable=True, isolate='info.GetIsolate()', used_in_private_script=False, async=False):
     """Returns an expression that converts a V8 value to a C++ value and stores it as a local value."""
 
     # FIXME: Support union type.
@@ -550,6 +550,12 @@ def v8_value_to_local_cpp_value(idl_type, extended_attributes, v8_value, variabl
     # v8::TryCatch.
     suffix = ''
 
+    if async:
+        suffix += '_ASYNC'
+        args.append('info')
+        if macro == 'TONATIVE_VOID_EXCEPTIONSTATE':

[haraken, 2014/07/31 07:54:47]

A slightly better condition would be:

  if idl_type.may_raise_exception_on_conversion:

[yhirano, 2014/08/01 02:27:57]

That condition can be true when macro is 'TOSTRING_DEFAULT', right?
I don't want to provide the ScriptState in such a case.

+            args.insert(0, 'ScriptState::current(%s)' % isolate)

[haraken, 2014/07/31 07:54:47]

Can we move the ScriptState argument to the last argument and just use
args.append() ? (Basically we put the ScriptState at the first argument, but it
would be more important to keep the IDL compiler logic simpler.)

[yhirano, 2014/08/01 02:27:57]

Done.

+
     if declare_variable:
         args.insert(0, this_cpp_type)
     else: