Fix strong mode errors in SVG

BUG=
R=alanknight@google.com

Review URL: https://codereview.chromium.org/1903893003 .

sdk/lib/html/dart2js/html_dart2js.dart

@@ -14836,9 +14836,8 @@ class Element extends Node implements NonDocumentTypeChildNode, GlobalEventHandl
   @DocsEditable()
   bool hidden;
 
-  @DomName('Element.isContentEditable')
-  @DocsEditable()
-  final bool isContentEditable;
+  // Using property as subclass shadows.
+  bool get isContentEditable => JS("bool", "#.isContentEditable", this);
 
   @DomName('Element.lang')
   @DocsEditable()
@@ -14963,10 +14962,8 @@ class Element extends Node implements NonDocumentTypeChildNode, GlobalEventHandl
   // Use implementation from Node.
   // final String _namespaceUri;
 
-  @JSName('outerHTML')
-  @DomName('Element.outerHTML')
-  @DocsEditable()
-  final String outerHtml;
+  // Using property as subclass shadows.
+  String get outerHtml => JS("String", "#.outerHTML", this);
 
   @JSName('scrollHeight')
   @DomName('Element.scrollHeight')

sdk/lib/svg/dart2js/svg_dart2js.dart

@@ -4646,12 +4646,8 @@ class StyleElement extends SvgElement {
   @Experimental() // untriaged
   final StyleSheet sheet;
 
-  // Shadowing definition.
-  String get title => JS("String", "#.title", this);
-
-  set title(String value) {
-    JS("void", "#.title = #", this, value);
-  }
+  // Use implementation from Element.
+  // final String title;
 
   @DomName('SVGStyleElement.type')
   @DocsEditable()
@@ -5085,12 +5081,8 @@ class SvgElement extends Element implements GlobalEventHandlers {
   // Use implementation from Element.
   // final CssStyleDeclaration style;
 
-  // Shadowing definition.
-  int get tabIndex => JS("int", "#.tabIndex", this);
-
-  set tabIndex(int value) {
-    JS("void", "#.tabIndex = #", this, value);
-  }
+  // Use implementation from Element.
+  // final int tabIndex;
 
   @DomName('SVGElement.viewportElement')
   @DocsEditable()

tools/dom/scripts/systemhtml.py

@@ -19,6 +19,21 @@ _logger = logging.getLogger('systemhtml')
 HTML_LIBRARY_NAMES = ['html', 'indexed_db', 'svg',
                       'web_audio', 'web_gl', 'web_sql']
 
+# The following two sets let us avoid shadowing fields with properties.
+# This information could be derived from the IDL files but would require
+# a significant refactor to compute accurately. Instead we manually compute
+# these sets based on manual triage of strong mode errors.
+_force_property_members = monitored.Set('systemhtml._force_property_members', [
+    'Element.outerHtml',
+    'Element.isContentEditable',
+    'AudioContext.createGain',
+    'AudioContext.createScriptProcessor',
+    ])
+_safe_to_ignore_shadowing_members = monitored.Set('systemhtml._safe_to_ignore_shadowing_members', [
+    'SVGElement.tabIndex',
+    'SVGStyleElement.title',
+    ])
+
 _js_custom_members = monitored.Set('systemhtml._js_custom_members', [
     'AudioBufferSourceNode.start',
     'AudioBufferSourceNode.stop',
@@ -895,8 +910,13 @@ class Dart2JSBackend(HtmlDartGenerator):
     #  is renamed.
     (super_attribute, super_attribute_interface) = self._FindShadowedAttribute(
         attribute)
+    if self._ForcePropertyMember(html_name):
+      self._members_emitter.Emit('\n  // Using property as subclass shadows.');
+      self._AddAttributeUsingProperties(attribute, html_name, read_only)
+      return
+
     if super_attribute:
-      if read_only:
+      if read_only or self._SafeToIgnoreShadowingMember(html_name):
         if attribute.type.id == super_attribute.type.id:
           # Compatible attribute, use the superclass property.  This works
           # because JavaScript will do its own dynamic dispatch.
@@ -1161,6 +1181,14 @@ class Dart2JSBackend(HtmlDartGenerator):
     member_name = '%s.%s' % (self._interface.doc_js_name, member_name)
     return member_name in _js_custom_members
 
+  def _ForcePropertyMember(self, member_name):
+    member_name = '%s.%s' % (self._interface.doc_js_name, member_name)
+    return member_name in _force_property_members
+
+  def _SafeToIgnoreShadowingMember(self, member_name):
+    member_name = '%s.%s' % (self._interface.doc_js_name, member_name)
+    return member_name in _safe_to_ignore_shadowing_members
+
   def _RenamingAnnotation(self, idl_name, member_name):
     if member_name != idl_name:
       return  "@JSName('%s')\n  " % idl_name