Enable strong mode in DDC, fix all warnings/errors

lib/src/compiler/reify_coercions.dart

 // Copyright (c) 2015, 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.
 
 import 'package:analyzer/analyzer.dart' as analyzer;
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/type.dart' show DartType;
 import 'package:analyzer/src/dart/ast/ast.dart' show FunctionBodyImpl;
 import 'package:analyzer/src/dart/ast/utilities.dart' show NodeReplacer;
 import 'package:analyzer/src/dart/element/type.dart' show DynamicTypeImpl;
@@ skipping 98 matching lines @@
     // We use an empty name in the AST, because the JS code generator only cares
     // about the target type. It does not look at the AST name.
     var typeName = new TypeName(AstBuilder.identifierFromString(''), null);
     typeName.type = toType;
     var cast = AstBuilder.asExpression(e, typeName);
     cast.staticType = toType;
     return cast;
   }
 
   /*=T*/ _clone/*<T extends AstNode>*/(/*=T*/ node) {
-    var copy = node.accept(cloner);
+    var copy = node.accept(cloner) as dynamic/*=T*/;
     ResolutionCopier.copyResolutionData(node, copy);
     return copy;
   }
 }
 
 class _TreeCloner extends analyzer.AstCloner {
   void _cloneProperties(AstNode clone, AstNode node) {
     if (clone != null) {
       CoercionInfo.set(clone, CoercionInfo.get(node));
       DynamicInvoke.set(clone, DynamicInvoke.get(node));
     }
   }
 
   @override
-  AstNode cloneNode(AstNode node) {
+  /*=E*/ cloneNode/*<E extends AstNode>*/(/*=E*/ node) {
     var clone = super.cloneNode(node);
     _cloneProperties(clone, node);
     return clone;
   }
 
   @override
-  List cloneNodeList(List list) {
+  List/*<E>*/ cloneNodeList/*<E extends AstNode>*/(NodeList/*<E>*/ list) {
     var clone = super.cloneNodeList(list);
     for (int i = 0, len = list.length; i < len; i++) {
       _cloneProperties(clone[i], list[i]);
     }
     return clone;
   }
 
   // TODO(jmesserly): ResolutionCopier is not copying this yet.
   @override
   BlockFunctionBody visitBlockFunctionBody(BlockFunctionBody node) {
@@ skipping 14 matching lines @@
 
   // TODO(jmesserly): workaround for
   // https://github.com/dart-lang/sdk/issues/26368
   @override
   TypeName visitTypeName(TypeName node) {
     var clone = super.visitTypeName(node);
     clone.type = node.type;
     return clone;
   }
 }