Create implementation file emitter in HtmlDartInterfaceGenerator.

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 dc5b3a204735cb32bcd56ce86be9c3620c89f2ba..2bdd9cd132705a0104f4f5c3fed5fed2d4248730 100644
--- a/lib/dom/scripts/systemnative.py
+++ b/lib/dom/scripts/systemnative.py
@@ -26,15 +26,9 @@ class NativeImplementationSystem(systembase.System):
     self._html_system = HtmlSystemShared(database)
     self._factory_provider_emitters = {}
 
-  def ProcessInterface(self, interface):
+  def ProcessInterface(self, interface, dart_implementation_emitter):
     interface_name = interface.id
 
-    if IsPureInterface(interface_name):
-      return None
-
-    dart_impl_path = self._FilePathForDartImplementation(interface_name)
-    self._dom_impl_files.append(dart_impl_path)
-
     cpp_header_path = self._FilePathForCppHeader(interface_name)
     self._cpp_header_files.append(cpp_header_path)
 
@@ -42,7 +36,7 @@ class NativeImplementationSystem(systembase.System):
     self._cpp_impl_files.append(cpp_impl_path)
 
     generator = NativeImplementationGenerator(self, interface,
-        self._emitters.FileEmitter(dart_impl_path),
+        dart_implementation_emitter,
         self._emitters.FileEmitter(cpp_header_path),
         self._emitters.FileEmitter(cpp_impl_path),
         self._BaseDefines(interface),
@@ -168,7 +162,10 @@ class NativeImplementationSystem(systembase.System):
   def Finish(self):
     pass
 
-  def _FilePathForDartImplementation(self, interface_name):
+  def HasImplementation(self, interface):
+    return not IsPureInterface(interface)
+
+  def FilePathForDartImplementation(self, interface_name):
     return os.path.join(self._output_dir, 'dart',
                         '%sImplementation.dart' % interface_name)