Implement cascaded calls.

lib/compiler/implementation/tree/nodes.dart

Index: lib/compiler/implementation/tree/nodes.dart
diff --git a/lib/compiler/implementation/tree/nodes.dart b/lib/compiler/implementation/tree/nodes.dart
index 71326fb607522bb2a342cc502a76c4d3aca8024f..993116cbf5d20f770dc62d27bd93f1cec4268d60 100644
--- a/lib/compiler/implementation/tree/nodes.dart
+++ b/lib/compiler/implementation/tree/nodes.dart
@@ -5,6 +5,8 @@
 interface Visitor<R> {
   R visitBlock(Block node);
   R visitBreakStatement(BreakStatement node);
+  R visitCascade(Cascade node);
+  R visitCascadeReceiver(CascadeReceiver node);
   R visitCatchBlock(CatchBlock node);
   R visitClassNode(ClassNode node);
   R visitConditional(Conditional node);
@@ -108,6 +110,8 @@ class Node implements Hashable {
 
   Block asBlock() => null;
   BreakStatement asBreakStatement() => null;
+  Cascade asCascade() => null;
+  CascadeReceiver asCascadeReceiver() => null;
   CatchBlock asCatchBlock() => null;
   ClassNode asClassNode() => null;
   Conditional asConditional() => null;
@@ -1561,6 +1565,39 @@ class TryStatement extends Statement {
   }
 }
 
+class Cascade extends Node {
+  final Node expression;
+  Cascade(this.expression);
+
+  Cascade asCascade() => this;
+  accept(Visitor visitor) => visitor.visitCascade(this);
+
+  void visitChildren(Visitor visitor) {
+    expression.accept(visitor);
+  }
+
+  Token getBeginToken() => expression.getBeginToken();
+
+  Token getEndToken() => expression.getEndToken();
+}
+
+class CascadeReceiver extends Node {
+  final Node expression;
+  final Token cascadeOperator;
+  CascadeReceiver(this.expression, this.cascadeOperator);
+
+  CascadeReceiver asCascadeReceiver() => this;
+  accept(Visitor visitor) => visitor.visitCascadeReceiver(this);
+
+  void visitChildren(Visitor visitor) {
+    expression.accept(visitor);
+  }
+
+  Token getBeginToken() => expression.getBeginToken();
+
+  Token getEndToken() => expression.getEndToken();
+}
+
 class CatchBlock extends Node {
   final NodeList formals;
   final Block block;