Start creating a MemberSet abstraction, and use it to fold getters/setters into field accesses.

lib/compiler/implementation/world.dart

Index: lib/compiler/implementation/world.dart
===================================================================
--- lib/compiler/implementation/world.dart	(revision 0)
+++ lib/compiler/implementation/world.dart	(revision 0)
@@ -0,0 +1,77 @@
+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// 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.
+
+class World {
+  final Map<ClassElement, Set<ClassElement>> subtypes;
+
+  World() : subtypes = new Map<ClassElement, Set<ClassElement>>();
+
+  void populate(Compiler compiler, Collection<LibraryElement> libraries) {
+    void addSubtypes(ClassElement cls) {
+      for (Type type in cls.allSupertypes) {
+        List<Element> subtypes = subtypes.putIfAbsent(
+          type.element,
+          () => <ClassElement>[]);
+        subtypes.add(cls);
+      }
+    }
+
+    libraries.forEach((LibraryElement library) {
+      for (Link<Element> link = library.topLevelElements;
+           !link.isEmpty();
+           link = link.tail) {
+        Element element = link.head;
+        if (!element.isClass()) continue;
+        ClassElement cls = element;
+        compiler.resolveClass(cls);
+        addSubtypes(cls);
+      }
+    });
+  }
+
+  /**
+   * Returns a [MemberSet] that contains the possible targets of a
+   * selector named [member] on a receiver whose type is [type].
+   */
+  MemberSet _memberSetFor(Type type, SourceString member) {
+    ClassElement cls = type.element;
+    MemberSet result = new MemberSet(member);
+    Element element = cls.lookupMember(member);
+    if (element !== null) result.add(element);
+
+    Set<ClassElement> subtypes = subtypes[cls];
+    if (subtypes !== null) {
+      for (ClassElement sub in subtypes) {
+        element = sub.lookupLocalMember(member);
+        if (element !== null) result.add(element);
+      }
+    }
+    return result;
+  }
+
+  bool isOnlyFields(Type type, SourceString member) {
+    MemberSet memberSet = _memberSetFor(type, member);
+    return !memberSet.isEmpty() && memberSet.hasJustFields();
+  }
+}
+
+/**
+ * A [MemberSet] contains all the possible targets for a selector.
+ */
+class MemberSet {
+  final Set<Element> elements;
+  final SourceString name;
+
+  MemberSet(SourceString this.name) : elements = new Set<Element>();
+
+  void add(Element element) {
+    elements.add(element);
+  }
+
+  bool isEmpty() => elements.isEmpty();
+
+  bool hasJustFields() {
+    return elements.every((Element element) => element.isField());
+  }
+}