Create fewer local v8::TryCatch objects in generated bindings code

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 466ab25e05ffe2237fc380efa6eff1c10e11ae9b..aee9e1abc42939d6e669eddb97e70af871d3428c 100644
--- a/Source/bindings/scripts/v8_types.py
+++ b/Source/bindings/scripts/v8_types.py
@@ -431,13 +431,13 @@ def v8_value_to_cpp_value_array_or_sequence(array_or_sequence_type, v8_value, in
     return expression
 
 
-def v8_value_to_local_cpp_value(idl_type, extended_attributes, v8_value, variable_name, index=None):
+def v8_value_to_local_cpp_value(idl_type, extended_attributes, v8_value, variable_name, index=None, declare_variable=True):
     """Returns an expression that converts a V8 value to a C++ value and stores it as a local value."""
     this_cpp_type = idl_type.cpp_type_args(extended_attributes=extended_attributes, used_as_argument=True)
 
     idl_type = idl_type.preprocessed_type
     cpp_value = v8_value_to_cpp_value(idl_type, extended_attributes, v8_value, index)
-    args = [this_cpp_type, variable_name, cpp_value]
+    args = [variable_name, cpp_value]
     if idl_type.base_type == 'DOMString' and not idl_type.array_or_sequence_type:
         macro = 'TOSTRING_VOID'
     elif idl_type.is_integer_type:
@@ -446,6 +446,12 @@ def v8_value_to_local_cpp_value(idl_type, extended_attributes, v8_value, variabl
     else:
         macro = 'TONATIVE_VOID'
 
+    if declare_variable:
+        args.insert(0, this_cpp_type)
+    else:
+        # Use a macro that assumes a previously declared local variable.
+        macro += '_NO_DECL'
+
     return '%s(%s)' % (macro, ', '.join(args))
 
 IdlType.v8_value_to_local_cpp_value = v8_value_to_local_cpp_value