IDL: Fix exception handling when converting V8 value to union/dictionary

Source/bindings/scripts/v8_dictionary.py

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Generate template contexts of dictionaries for both v8 bindings and
 implementation classes that are used by blink's core/modules.
 """
 
 import operator
 from idl_types import IdlType
@@ skipping 103 matching lines @@
         'is_interface_type': idl_type.is_interface_type and not idl_type.is_dictionary,
         'is_nullable': idl_type.is_nullable,
         'is_object': unwrapped_idl_type.name == 'Object',
         'name': member.name,
         'setter_name': setter_name_for_dictionary_member(member),
         'null_setter_name': null_setter_name_for_dictionary_member(member),
         'use_output_parameter_for_result': unwrapped_idl_type.use_output_parameter_for_result,
         'v8_default_value': v8_default_value,
         'v8_value_to_local_cpp_value': unwrapped_idl_type.v8_value_to_local_cpp_value(
             member.extended_attributes, member.name + 'Value',
-            member.name, isolate='isolate', restricted_float=restricted_float),
+            member.name, isolate='isolate', restricted_float=restricted_float,
+            needs_exception_state_for_string=True, no_throw=True),
     }
 
 
 # Context for implementation classes
 
 def dictionary_impl_context(dictionary, interfaces_info):
     def remove_duplicate_members(members):
         # When [ImplementedAs] is used, cpp_name can conflict. For example,
         # dictionary D { long foo; [ImplementedAs=foo, DeprecateAs=Foo] long oldFoo; };
         # This function removes such duplications, checking they have the same type.
@@ skipping 61 matching lines @@
         'getter_expression': getter_expression(),
         'has_method_expression': has_method_expression(),
         'has_method_name': has_method_name_for_dictionary_member(member),
         'is_object': is_object,
         'is_traceable': idl_type.is_traceable,
         'member_cpp_type': member_cpp_type(),
         'null_setter_name': null_setter_name_for_dictionary_member(member),
         'rvalue_cpp_type': idl_type.cpp_type_args(used_as_rvalue_type=True),
         'setter_name': setter_name_for_dictionary_member(member),
     }