Let the inferrer know that lazy variables can also be null incase their initializer throws.

sdk/lib/_internal/compiler/implementation/tree/nodes.dart

Index: sdk/lib/_internal/compiler/implementation/tree/nodes.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/tree/nodes.dart	(revision 27658)
+++ sdk/lib/_internal/compiler/implementation/tree/nodes.dart	(working copy)
@@ -174,6 +174,7 @@
   Modifiers asModifiers() => null;
   NamedArgument asNamedArgument() => null;
   NamedMixinApplication asNamedMixinApplication() => null;
+  NewExpression asNewExpression() => null;
   NodeList asNodeList() => null;
   Operator asOperator() => null;
   ParenthesizedExpression asParenthesizedExpression() => null;
@@ -473,6 +474,8 @@
 
   NewExpression([this.newToken, this.send]);
 
+  NewExpression asNewExpression() => this;
+
   accept(Visitor visitor) => visitor.visitNewExpression(this);
 
   visitChildren(Visitor visitor) {