Changes dart2js to warn at reified usage of method type variables.

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

Index: pkg/compiler/lib/src/resolution/members.dart
diff --git a/pkg/compiler/lib/src/resolution/members.dart b/pkg/compiler/lib/src/resolution/members.dart
index a69b35950f82b7543c57db1a381905fd582867f6..a382b7510bc540a71a507c5b220adec4bd9988cb 100644
--- a/pkg/compiler/lib/src/resolution/members.dart
+++ b/pkg/compiler/lib/src/resolution/members.dart
@@ -1121,6 +1121,14 @@ class ResolverVisitor extends MappingVisitor<ResolutionResult> {
       type = resolveTypeAnnotation(typeNode);
       sendStructure = new IsStructure(type);
     }
+
+    // GENERIC_METHODS: Method type variables are not reified so we must warn
+    // about the error which will occur at runtime.
+    if (type is MethodTypeVariableType) {
+      reporter.reportWarningMessage(
+          node, MessageKind.TYPE_VARIABLE_FROM_METHOD_NOT_REIFIED);
+    }
+
     registry.registerTypeUse(new TypeUse.isCheck(type));
     registry.registerSendStructure(node, sendStructure);
     return const NoneResult();
@@ -1133,6 +1141,14 @@ class ResolverVisitor extends MappingVisitor<ResolutionResult> {
 
     Node typeNode = node.arguments.head;
     DartType type = resolveTypeAnnotation(typeNode);
+
+    // GENERIC_METHODS: Method type variables are not reified so we must warn
+    // about the error which will occur at runtime.
+    if (type is MethodTypeVariableType) {
+      reporter.reportWarningMessage(
+          node, MessageKind.TYPE_VARIABLE_FROM_METHOD_NOT_REIFIED);
+    }
+
     registry.registerTypeUse(new TypeUse.asCast(type));
     registry.registerSendStructure(node, new AsStructure(type));
     return const NoneResult();
@@ -1888,6 +1904,12 @@ class ResolverVisitor extends MappingVisitor<ResolutionResult> {
       // TODO(johnniwinther): Clean up registration of elements and selectors
       // for this case.
     } else {
+      // GENERIC_METHODS: Method type variables are not reified so we must warn
+      // about the error which will occur at runtime.
+      if (element.type is MethodTypeVariableType) {
+        reporter.reportWarningMessage(
+            node, MessageKind.TYPE_VARIABLE_FROM_METHOD_NOT_REIFIED);
+      }
       semantics = new StaticAccess.typeParameterTypeLiteral(element);
     }