Test ResolutionImpact equivalence.

pkg/compiler/lib/src/common/resolution.dart

Index: pkg/compiler/lib/src/common/resolution.dart
diff --git a/pkg/compiler/lib/src/common/resolution.dart b/pkg/compiler/lib/src/common/resolution.dart
index 1f099153074fc537ac488a2fd8b831e85d540645..95b71482ec756505f538e7da53b1f3280d10d80a 100644
--- a/pkg/compiler/lib/src/common/resolution.dart
+++ b/pkg/compiler/lib/src/common/resolution.dart
@@ -145,6 +145,10 @@ class MapLiteralUse {
         isConstant == other.isConstant &&
         isEmpty == other.isEmpty;
   }
+
+  String toString() {
+    return 'MapLiteralUse($type,isConstant:$isConstant,isEmpty:$isEmpty)';
+  }
 }
 
 /// A use of a list literal seen during resolution.
@@ -170,6 +174,10 @@ class ListLiteralUse {
         isConstant == other.isConstant &&
         isEmpty == other.isEmpty;
   }
+
+  String toString() {
+    return 'ListLiteralUse($type,isConstant:$isConstant,isEmpty:$isEmpty)';
+  }
 }
 
 // TODO(johnniwinther): Rename to `Resolver` or `ResolverContext`.
@@ -178,6 +186,8 @@ abstract class Resolution {
   DiagnosticReporter get reporter;
   CoreTypes get coreTypes;
 
+  bool retainCaches;
+
   void resolveTypedef(TypedefElement typdef);
   void resolveClass(ClassElement cls);
   void registerClass(ClassElement cls);
@@ -190,6 +200,9 @@ abstract class Resolution {
   ResolutionWorkItem createWorkItem(
       Element element, ItemCompilationContext compilationContext);
 
+  /// Returns `true` if the [ResolutionImpact] for [element] is cached.
+  bool hasResolutionImpact(Element element);
+
   /// Returns the precomputed [ResolutionImpact] for [element].
   ResolutionImpact getResolutionImpact(Element element);