Added the CanvasImageSource interface, which all types that a canvas can draw

tools/dom/templates/html/impl/impl_HTMLVideoElement.darttemplate

Index: tools/dom/templates/html/impl/impl_HTMLVideoElement.darttemplate
diff --git a/tools/dom/templates/html/dartium/dart_implementation.darttemplate b/tools/dom/templates/html/impl/impl_HTMLVideoElement.darttemplate
similarity index 69%
copy from tools/dom/templates/html/dartium/dart_implementation.darttemplate
copy to tools/dom/templates/html/impl/impl_HTMLVideoElement.darttemplate
index f0c067d7aee653d224cf9239d12d96d9139671ed..59cd0f738efaaa9f2d09cde1823791bfab4ce35a 100644
--- a/tools/dom/templates/html/dartium/dart_implementation.darttemplate
+++ b/tools/dom/templates/html/impl/impl_HTMLVideoElement.darttemplate
@@ -2,11 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// WARNING: Do not edit - generated code.
-
 part of $LIBRARYNAME;
 
-@DocsEditable
-$(ANNOTATIONS)class $CLASSNAME$EXTENDS$IMPLEMENTS {
+$(ANNOTATIONS)class $CLASSNAME$EXTENDS implements CanvasImageSource$IMPLEMENTS$NATIVESPEC {
 $!MEMBERS
 }