API functions returning Promises should not throw exceptions.

Source/bindings/scripts/v8_methods.py

Index: Source/bindings/scripts/v8_methods.py
diff --git a/Source/bindings/scripts/v8_methods.py b/Source/bindings/scripts/v8_methods.py
index 9e92e0ed43d273adc1b054f1be904578a42c0037..c23b9ecf30da4241a5e044fe51080ef6b3310ff1 100644
--- a/Source/bindings/scripts/v8_methods.py
+++ b/Source/bindings/scripts/v8_methods.py
@@ -51,7 +51,7 @@ CUSTOM_REGISTRATION_EXTENDED_ATTRIBUTES = frozenset([
 ])
 
 
-def argument_needs_try_catch(argument):
+def argument_needs_try_catch(argument, async):
     idl_type = argument.idl_type
     base_type = not idl_type.native_array_element_type and idl_type.base_type
 
@@ -64,7 +64,7 @@ def argument_needs_try_catch(argument):
         # String and enumeration arguments converted using one of the
         # TOSTRING_* macros in Source/bindings/core/v8/V8BindingMacros.h don't
         # use a v8::TryCatch.
-        (base_type == 'DOMString' and not argument.is_variadic))
+        (base_type == 'DOMString' and not argument.is_variadic and not async))
 
 
 def use_local_result(method):
@@ -83,6 +83,7 @@ def method_context(interface, method):
     idl_type = method.idl_type
     is_static = method.is_static
     name = method.name
+    async = idl_type.name == 'Promise'
 
     idl_type.add_includes_for_type()
     this_cpp_value = cpp_value(interface, method, len(arguments))
@@ -122,7 +123,7 @@ def method_context(interface, method):
         'DoNotCheckSecurity' not in extended_attributes)
     is_raises_exception = 'RaisesException' in extended_attributes
 
-    arguments_need_try_catch = any(argument_needs_try_catch(argument)
+    arguments_need_try_catch = any(argument_needs_try_catch(argument, async)
                                    for argument in arguments)
 
     return {
@@ -243,6 +244,7 @@ def argument_context(interface, method, argument, index):
         'v8_set_return_value': v8_set_return_value(interface.name, method, this_cpp_value),
         'v8_set_return_value_for_main_world': v8_set_return_value(interface.name, method, this_cpp_value, for_main_world=True),
         'v8_value_to_local_cpp_value': v8_value_to_local_cpp_value(argument, index),
+        'v8_value_to_local_cpp_value_async': v8_value_to_local_cpp_value(argument, index, async=True),
         'vector_type': v8_types.cpp_ptr_type('Vector', 'HeapVector', idl_type.gc_type),
     }
 
@@ -345,27 +347,35 @@ def v8_set_return_value(interface_name, method, cpp_value, for_main_world=False)
     return idl_type.v8_set_return_value(cpp_value, extended_attributes, script_wrappable=script_wrappable, release=release, for_main_world=for_main_world)
 
 
-def v8_value_to_local_cpp_variadic_value(argument, index):
+def v8_value_to_local_cpp_variadic_value(argument, index, async):
     assert argument.is_variadic
     idl_type = argument.idl_type
 
-    macro = 'TONATIVE_VOID_INTERNAL'
+    suffix = ''
+
+    macro = 'TONATIVE_VOID'
     macro_args = [
       argument.name,
       'toNativeArguments<%s>(info, %s)' % (idl_type.cpp_type, index),
     ]
 
-    return '%s(%s)' % (macro, ', '.join(macro_args))
+    if async:
+        suffix += '_ASYNC'
+        macro_args.append('info')
+
+    suffix += '_INTERNAL'
+
+    return '%s%s(%s)' % (macro, suffix, ', '.join(macro_args))
 
 
-def v8_value_to_local_cpp_value(argument, index):
+def v8_value_to_local_cpp_value(argument, index, async=False):
     extended_attributes = argument.extended_attributes
     idl_type = argument.idl_type
     name = argument.name
     if argument.is_variadic:
-        return v8_value_to_local_cpp_variadic_value(argument, index)
+        return v8_value_to_local_cpp_variadic_value(argument, index, async)
     return idl_type.v8_value_to_local_cpp_value(extended_attributes, 'info[%s]' % index,
-                                                name, index=index, declare_variable=False)
+                                                name, index=index, declare_variable=False, async=async)
 
 
 ################################################################################