Propagate type inference through variable gets.

pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart

Index: pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
diff --git a/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart b/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
index 1d39d0e0e14f9e9fa3092fc7b919dfc3ef829355..1512e67fe83730ef8ef8039d8eca11b4e9980805 100644
--- a/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
+++ b/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
@@ -563,7 +563,7 @@ abstract class TypeInferrerImpl<S, E, V, F> extends TypeInferrer<S, E, V, F> {
       TypePromotionFact<V> typePromotionFact,
       TypePromotionScope typePromotionScope,
       int offset,
-      DartType declaredType,
+      DartType declaredOrInferredType,
       void setPromotedType(DartType type)) {
     DartType promotedType = typePromoter.computePromotedType(
         typePromotionFact, typePromotionScope, mutatedInClosure);
@@ -575,9 +575,7 @@ abstract class TypeInferrerImpl<S, E, V, F> extends TypeInferrer<S, E, V, F> {
             ? new InstrumentationValueForType(promotedType)
             : const InstrumentationValueLiteral('none'));
     setPromotedType(promotedType);
-    return typeNeeded
-        ? (promotedType ?? declaredType ?? const DynamicType())
-        : null;
+    return typeNeeded ? (promotedType ?? declaredOrInferredType) : null;
   }
 
   DartType inferVariableSet(