Cache metadata constants for make benefit of glorious try/poi/forget_element_test

pkg/compiler/lib/src/js_backend/constant_handler_javascript.dart

 // Copyright (c) 2014, 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.
 
 part of js_backend;
 
 /// [ConstantCompilerTask] for compilation of constants for the JavaScript
 /// backend.
 ///
 /// Since this task needs to distinguish between frontend and backend constants
@@ skipping 97 matching lines @@
   final Set<ConstantValue> compiledConstants = new Set<ConstantValue>();
 
   // TODO(johnniwinther): Move this to the backend constant handler.
   /** Caches the statics where the initial value cannot be eagerly compiled. */
   final Set<VariableElement> lazyStatics = new Set<VariableElement>();
 
   // Constants computed for constant expressions.
   final Map<Node, ConstantExpression> nodeConstantMap =
       new Map<Node, ConstantExpression>();
 
+  // Constants computed for metadata.
+  // TODO(johnniwinther): Remove this when no longer used by
+  // poi/forget_element_test.
+  final Map<MetadataAnnotation, ConstantExpression> metadataConstantMap =
+      new Map<MetadataAnnotation, ConstantExpression>();
+
   JavaScriptConstantCompiler(Compiler compiler)
       : super(compiler, JAVA_SCRIPT_CONSTANT_SYSTEM);
 
   ConstantExpression compileVariableWithDefinitions(
       VariableElement element, TreeElements definitions,
       {bool isConst: false, bool checkType: true}) {
     if (!isConst && lazyStatics.contains(element)) {
       return null;
     }
     ConstantExpression value = super.compileVariableWithDefinitions(
@@ skipping 76 matching lines @@
     if (constant != null) {
       return constant;
     }
     return definitions.getConstant(node);
   }
 
   ConstantValue getConstantValueForMetadata(MetadataAnnotation metadata) {
     return getConstantValue(metadata.constant);
   }
 
+  @override
+  ConstantExpression compileMetadata(
+      MetadataAnnotation metadata, Node node, TreeElements elements) {
+      ConstantExpression constant =
+          super.compileMetadata(metadata, node, elements);
+      metadataConstantMap[metadata] = constant;
+      return constant;
+  }
+
   void forgetElement(Element element) {
     super.forgetElement(element);
     const ForgetConstantElementVisitor().visit(element, this);
     if (element is AstElement && element.hasNode) {
       element.node.accept(new ForgetConstantNodeVisitor(this));
     }
   }
 }
 
 class ForgetConstantElementVisitor
     extends BaseElementVisitor<dynamic, JavaScriptConstantCompiler> {
   const ForgetConstantElementVisitor();
 
   void visitElement(Element e, JavaScriptConstantCompiler constants) {
     for (MetadataAnnotation data in e.implementation.metadata) {
+      constants.metadataConstantMap.remove(data);
       if (data.hasNode) {
         data.node.accept(new ForgetConstantNodeVisitor(constants));
       }
     }
   }
 
   void visitFunctionElement(
       FunctionElement e, JavaScriptConstantCompiler constants) {
     super.visitFunctionElement(e, constants);
     if (e.hasFunctionSignature) {
@@ skipping 14 matching lines @@
     // TODO(ahe): This doesn't belong here. Rename this class and generalize.
     var closureClassMap = constants
         .compiler.closureToClassMapper.closureMappingCache
         .remove(node);
     if (closureClassMap != null) {
       closureClassMap
           .removeMyselfFrom(constants.compiler.enqueuer.codegen.universe);
     }
   }
 }