Support WebIDL optional default value syntax

Source/bindings/scripts/idl_definitions.py

Index: Source/bindings/scripts/idl_definitions.py
diff --git a/Source/bindings/scripts/idl_definitions.py b/Source/bindings/scripts/idl_definitions.py
index 2230c8f6e207153d8145a7d7dca1560077f1bf7b..94b006c49eb6d813bb8c010a11afdf952e5094f6 100644
--- a/Source/bindings/scripts/idl_definitions.py
+++ b/Source/bindings/scripts/idl_definitions.py
@@ -470,6 +470,7 @@ class IdlOperation(TypedObject):
 
 class IdlArgument(TypedObject):
     def __init__(self, node):
+        self.default_value = None
         self.extended_attributes = {}
         self.idl_type = None
         self.is_optional = node.GetProperty('OPTIONAL')  # syntax: (optional T)
@@ -488,6 +489,8 @@ class IdlArgument(TypedObject):
                 if child_name != '...':
                     raise ValueError('Unrecognized Argument node; expected "...", got "%s"' % child_name)
                 self.is_variadic = child.GetProperty('ELLIPSIS') or False
+            elif child_class == 'Default':
+                self.default_value = default_node_to_default_value(child)
             else:
                 raise ValueError('Unrecognized node class: %s' % child_class)
 
@@ -504,6 +507,19 @@ def arguments_node_to_arguments(node):
 
 
 ################################################################################
+# Default value
+################################################################################
+
+def default_node_to_default_value(node):
+    # FIXME: IDL parser currently outputs literal values inconsistently(crbug.com/374178).

[Nils Barth (inactive), 2014/06/02 02:48:34]

Please use complete URLs (so syntax matching detects them).
In fact, once it's consistent, you can remove this function, since it's just a
single expression!

So the comment should be something like:
    # FIXME: Should be: return node.GetProperty('VALUE') (inlined)
    # but IDL parser currently outputs literal values inconsistently
    # http://crbug.com/374178

+    # This function should return node.GetProperty('VALUE') once this issue is fixed.
+    if (node.GetProperty('TYPE') == "boolean" or

[Nils Barth (inactive), 2014/06/02 02:48:34]

Single quotes.

+       node.GetProperty('TYPE') == "float"):

[Nils Barth (inactive), 2014/06/02 02:48:34]

You can use |in| for checking against a list:
node.GetProperty('TYPE') in ('boolean', 'float')
Slick, eh?

[Nils Barth (inactive), 2014/06/02 02:54:15]

BTW, since it's probably unfamiliar:
You can also use |in| for substring testing!
https://docs.python.org/2/library/stdtypes.html#index-22

+        return node.GetProperty('VALUE')
+    return node.GetName()
+
+
+################################################################################
 # Extended attributes
 ################################################################################