cpsir: triage remainder of html test suite, fix a couple.

tools/dom/scripts/dartmetadata.py

Index: tools/dom/scripts/dartmetadata.py
diff --git a/tools/dom/scripts/dartmetadata.py b/tools/dom/scripts/dartmetadata.py
index 3e16cf72d5f19a4a2474403f02bf2812f5b81567..e0d28aba27dc5f30bbf748b7788bd85c641dedf7 100644
--- a/tools/dom/scripts/dartmetadata.py
+++ b/tools/dom/scripts/dartmetadata.py
@@ -126,13 +126,13 @@ _dart2js_annotations = monitored.Dict('dartmetadata._dart2js_annotations', {
     # addEventListener on the target, so we avoid
     'Event.currentTarget': [
       "@Creates('Null')",
-      "@Returns('EventTarget|=Object')",
+      "@Returns('EventTarget|=Object|Null')",
     ],
 
     # Only nodes in the DOM bubble and have target !== currentTarget.
     'Event.target': [
       "@Creates('Node')",
-      "@Returns('EventTarget|=Object')",
+      "@Returns('EventTarget|=Object|Null')",
     ],
 
     'File.lastModifiedDate': [
@@ -273,7 +273,7 @@ _dart2js_annotations = monitored.Dict('dartmetadata._dart2js_annotations', {
 
     'MouseEvent.relatedTarget': [
       "@Creates('Node')",
-      "@Returns('EventTarget|=Object')",
+      "@Returns('EventTarget|=Object|Null')",
     ],
 
     'PopStateEvent.state': [