After a dynamic call, refine the receiver type by looking at the potential targets of that call.

sdk/lib/_internal/compiler/implementation/universe/universe.dart

Index: sdk/lib/_internal/compiler/implementation/universe/universe.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/universe/universe.dart	(revision 22031)
+++ sdk/lib/_internal/compiler/implementation/universe/universe.dart	(working copy)
@@ -91,6 +91,29 @@
   bool hasFieldSetter(Element member, Compiler compiler) {
     return fieldSetters.contains(member);
   }
+
+  bool onlyReachesFinalFields(Selector getterSelector, Compiler compiler) {
+    assert(getterSelector.isGetter());
+    Selector setterSelector = new Selector.setterFrom(getterSelector);
+    if (getterSelector.mask != null) {
+      setterSelector = new TypedSelector(getterSelector.mask, setterSelector);
+    }
+
+    bool hasInvokedSetter = invokedSetters[setterSelector.name] != null
+        && !invokedSetters[setterSelector.name].isEmpty;
+
+    Iterable<Element> targets =
+        compiler.world.allFunctions.filter(setterSelector);
+    for (Element target in targets) {
+      assert(!target.isAbstractField());
+      // Final fields have been filtered out.
+      assert(!target.modifiers.isFinal());
+      if (target.isNative()) return false;
+      if (!target.isField()) return false;
+      if (hasInvokedSetter) return false;
+    }
+    return true;
+  }
 }
 
 class SelectorKind {
@@ -140,6 +163,9 @@
   Selector.setter(SourceString name, LibraryElement library)
       : this(SelectorKind.SETTER, name, library, 1);
 
+  Selector.setterFrom(Selector selector)
+      : this(SelectorKind.SETTER, selector.name, selector.library, 1);
+
   Selector.unaryOperator(SourceString name)
       : this(SelectorKind.OPERATOR,
              Elements.constructOperatorName(name, true),