Split backend.AddMembers call into series of backend.AddAtribute/backend.AddOperation calls.

lib/dom/scripts/systemnative.py

Index: lib/dom/scripts/systemnative.py
diff --git a/lib/dom/scripts/systemnative.py b/lib/dom/scripts/systemnative.py
index 6614acbe5b461585b5ec4cbdcd7b3a7b400dbbeb..f9bfcc1888bb43bf98a78d2aeb59d462ba5abe61 100644
--- a/lib/dom/scripts/systemnative.py
+++ b/lib/dom/scripts/systemnative.py
@@ -193,11 +193,12 @@ class NativeImplementationGenerator(systembase.BaseGenerator):
   def SetImplementationEmitter(self, implementation_emitter):
     self._dart_impl_emitter = implementation_emitter
 
-  def AddMergedMembers(self, merged_interface):
+  def MergedMembersGenerator(self):
     # We could not add merged functions to implementation class because
     # underlying c++ object doesn't implement them. Merged functions are
     # generated on merged interface implementation instead.
-    pass
+    # Return dummy generator.
+    return systembase.BaseGenerator(self._database, self._interface)
 
   def StartInterface(self):
     # Create emitters for c++ implementation.
@@ -469,10 +470,6 @@ class NativeImplementationGenerator(systembase.BaseGenerator):
 
     return False
 
-  def AddConstant(self, constant):
-    # Constants are already defined on the interface.
-    pass
-
   def AddAttribute(self, attribute):
     getter = attribute
     setter = attribute if not systembase.IsReadOnly(attribute) else None