Reapply "reflectType() dynamic type arguments support (#26012)"

runtime/lib/mirrors_impl.dart

Index: runtime/lib/mirrors_impl.dart
diff --git a/runtime/lib/mirrors_impl.dart b/runtime/lib/mirrors_impl.dart
index fe1c56ecdeb2726c023103dcfe542f93f8ab8668..f152adbc7334cffa00596224455530aecd15e020 100644
--- a/runtime/lib/mirrors_impl.dart
+++ b/runtime/lib/mirrors_impl.dart
@@ -1645,6 +1645,8 @@ class _Mirrors {
       native "Mirrors_makeLocalClassMirror";
   static TypeMirror makeLocalTypeMirror(Type key)
       native "Mirrors_makeLocalTypeMirror";
+  static Type instantiateGenericType(Type key, typeArguments)
+      native "Mirrors_instantiateGenericType";
 
   static Expando<ClassMirror> _declarationCache = new Expando("ClassMirror");
   static Expando<TypeMirror> _instantiationCache = new Expando("TypeMirror");
@@ -1661,7 +1663,10 @@ class _Mirrors {
     return classMirror;
   }
 
-  static TypeMirror reflectType(Type key) {
+  static TypeMirror reflectType(Type key, [List<Type> typeArguments]) {
+    if (typeArguments != null) {
+      key = _instantiateType(key, typeArguments);
+    }
     var typeMirror = _instantiationCache[key];
     if (typeMirror == null) {
       typeMirror = makeLocalTypeMirror(key);
@@ -1672,4 +1677,12 @@ class _Mirrors {
     }
     return typeMirror;
   }
+
+  static Type _instantiateType(Type key, List<Type> typeArguments) {
+    if (typeArguments.isEmpty) {
+      throw new ArgumentError.value(
+        typeArguments, 'typeArguments', 'Type arguments list cannot be empty.');
+    }
+    return instantiateGenericType(key, typeArguments.toList(growable: false));
+  }
 }