Enable strong mode in DDC, fix all warnings/errors

lib/src/compiler/side_effect_analysis.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/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/src/generated/constant.dart';
 import 'package:analyzer/src/generated/error.dart'
     show AnalysisErrorListener, ErrorReporter;
@@ skipping 20 matching lines @@
 /// This method is conservative: it should never return `true` unless it is
 /// certain the [node] is stateless, because generated code may rely on the
 /// correctness of a `true` value. However it may return `false` for things
 /// that are in fact, stateless.
 bool isStateless(FunctionBody function, Expression node, [AstNode context]) {
   // `this` and `super` cannot be reassigned.
   if (node is ThisExpression || node is SuperExpression) return true;
   if (node is Identifier) {
     var e = node.staticElement;
     if (e is PropertyAccessorElement) {
-      e = e.variable;
+      e = (e as PropertyAccessorElement).variable;
     }
     if (e is VariableElement && !e.isSynthetic) {
       if (e.isFinal) return true;
       if (e is LocalVariableElement || e is ParameterElement) {
         // make sure the local isn't mutated in the context.
         return !_isPotentiallyMutated(function, e, context);
       }
     }
   }
   return false;
@@ skipping 77 matching lines @@
     // ConstantEvaluator will not compute constants for non-const fields,
     // so run ConstantVisitor for those to figure out if the initializer is
     // actually a constant (and therefore side effect free to evaluate).
     assert(!field.isConst);
 
     var initializer = field.initializer;
     if (initializer == null) return null;
     return initializer.accept(_constantVisitor);
   }
 }