Enable strong mode in DDC, fix all warnings/errors

lib/src/compiler/element_helpers.dart

 // Copyright (c) 2016, 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.
 
 /// Helpers for Analyzer's Element model and corelib model.
 
 import 'package:analyzer/dart/ast/ast.dart'
     show
         ConstructorDeclaration,
         Expression,
         FunctionBody,
         FunctionExpression,
         MethodDeclaration,
         MethodInvocation,
         SimpleIdentifier;
 import 'package:analyzer/dart/element/element.dart'
     show Element, ExecutableElement, FunctionElement;
 import 'package:analyzer/dart/element/type.dart'
     show DartType, InterfaceType, ParameterizedType;
 import 'package:analyzer/src/dart/element/type.dart' show DynamicTypeImpl;
-import 'package:analyzer/src/generated/constant.dart' show DartObject;
+import 'package:analyzer/src/generated/constant.dart'
+    show DartObject, DartObjectImpl;
 
 class Tuple2<T0, T1> {
   final T0 e0;
   final T1 e1;
   Tuple2(this.e0, this.e1);
 }
 
 /*=T*/ fillDynamicTypeArgs/*<T extends DartType>*/(/*=T*/ t) {
   if (t is ParameterizedType) {
-    var dyn = new List.filled(t.typeArguments.length, DynamicTypeImpl.instance);
-    return t.substitute2(dyn, t.typeArguments);
+    var pt = t as ParameterizedType;
+    var dyn = new List<DartType>.filled(
+        pt.typeArguments.length, DynamicTypeImpl.instance);
+    return pt.substitute2(dyn, pt.typeArguments) as dynamic/*=T*/;
   }
   return t;
 }
 
 /// Given an annotated [node] and a [test] function, returns the first matching
 /// constant valued annotation.
 ///
 /// For example if we had the ClassDeclaration node for `FontElement`:
 ///
 ///    @js.JS('HTMLFontElement')
 ///    @deprecated
 ///    class FontElement { ... }
 ///
 /// We could match `@deprecated` with a test function like:
 ///
 ///    (v) => v.type.name == 'Deprecated' && v.type.element.library.isDartCore
 ///
-DartObject findAnnotation(Element element, bool test(DartObject value)) {
+DartObject findAnnotation(Element element, bool test(DartObjectImpl value)) {
   for (var metadata in element.metadata) {
     var value = metadata.constantValue;
     if (value != null && test(value)) return value;
   }
   return null;
 }
 
 /// Searches all supertype, in order of most derived members, to see if any
 /// [match] a condition. If so, returns the first match, otherwise returns null.
 InterfaceType findSupertype(InterfaceType type, bool match(InterfaceType t)) {
@@ skipping 48 matching lines @@
 ///       final String name;
 ///       // ...
 ///       const MyAnnotation(this.name/*, ... other params ... */);
 ///     }
 ///
 ///     @MyAnnotation('FooBar')
 ///     main() { ... }
 ///
 /// If we match the annotation for the `@MyAnnotation('FooBar')` this will
 /// return the string 'FooBar'.
-String getAnnotationName(Element element, bool match(DartObject value)) =>
+String getAnnotationName(Element element, bool match(DartObjectImpl value)) =>
     findAnnotation(element, match)?.getField('name')?.toStringValue();