Better support for the case of typed arrays inheriting from other typed arrays.

lib/dom/scripts/generator.py

Index: lib/dom/scripts/generator.py
diff --git a/lib/dom/scripts/generator.py b/lib/dom/scripts/generator.py
index cb7adfdab98cca1ab7dfe672cec221e32620121f..2e055466209fa3eab1a8b0e0c45139da342a6c9e 100644
--- a/lib/dom/scripts/generator.py
+++ b/lib/dom/scripts/generator.py
@@ -85,6 +85,27 @@ dom_frog_native_bodies = {
 def IsPrimitiveType(type_name):
   return isinstance(GetIDLTypeInfo(type_name), PrimitiveIDLTypeInfo)
 
+def ListImplementationInfo(interface, database):
+  """Returns a tuple (elment_type, requires_indexer).
+  If interface do not have to implement List, element_type is None.
+  Otherwise element_type is list element type and requires_indexer
+  is true iff this interface implementation must have indexer and
+  false otherwise.  False means that interface implementation
+  inherits indexer and may just reuse it."""
+  element_type = MaybeListElementType(interface)
+  if element_type:
+    return (element_type, True)
+
+  for parent in interface.parents:
+    if database.HasInterface(parent.type.id):
+      parent_interface = database.GetInterface(parent.type.id)
+      (element_type, _) = ListImplementationInfo(parent_interface, database)
+      if element_type:
+        return (element_type, False)
+
+  return (None, None)
+
+
 def MaybeListElementTypeName(type_name):
   """Returns the List element type T from string of form "List<T>", or None."""
   match = re.match(r'sequence<(\w*)>$', type_name)
@@ -108,10 +129,26 @@ def MaybeTypedArrayElementType(interface):
   """
   # Typed arrays implement ArrayBufferView and List<T>.
   for parent in interface.parents:
-    if  parent.type.id == 'ArrayBufferView':
+    if parent.type.id == 'ArrayBufferView':
       return MaybeListElementType(interface)
   return None
 
+def MaybeTypedArrayElementTypeInHierarchy(interface, database):
+  """Returns the typed array element type, or None in interface is not a
+  TypedArray.  Checks the whole parent hierarchy.
+  """
+  element_type = MaybeTypedArrayElementType(interface)
+  if element_type:
+    return element_type
+  for parent in interface.parents:
+    if database.HasInterface(parent.type.id):
+      parent_interface = database.GetInterface(parent.type.id)
+      element_type = MaybeTypedArrayElementType(parent_interface)
+      if element_type:
+        return element_type
+
+  return None
+
 def MakeNativeSpec(javascript_binding_name):
   if javascript_binding_name in _frog_dom_custom_native_specs:
     return _frog_dom_custom_native_specs[javascript_binding_name]