Remove js.Sequence and use binary comma operator instead.

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

Index: sdk/lib/_internal/compiler/implementation/js/nodes.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js/nodes.dart b/sdk/lib/_internal/compiler/implementation/js/nodes.dart
index d19ae570374b7285b0c73088aea1b23fe04a5958..db260dbdccb1bc9f10e561bdf05d86b0d89467a9 100644
--- a/sdk/lib/_internal/compiler/implementation/js/nodes.dart
+++ b/sdk/lib/_internal/compiler/implementation/js/nodes.dart
@@ -31,7 +31,6 @@ abstract class NodeVisitor<T> {
   T visitBlob(Blob node);
   T visitLiteralExpression(LiteralExpression node);
   T visitVariableDeclarationList(VariableDeclarationList node);
-  T visitSequence(Sequence node);
   T visitAssignment(Assignment node);
   T visitVariableInitialization(VariableInitialization node);
   T visitConditional(Conditional cond);
@@ -113,7 +112,6 @@ class BaseVisitor<T> implements NodeVisitor<T> {
   T visitLiteralExpression(LiteralExpression node) => visitExpression(node);
   T visitVariableDeclarationList(VariableDeclarationList node)
       => visitExpression(node);
-  T visitSequence(Sequence node) => visitExpression(node);
   T visitAssignment(Assignment node) => visitExpression(node);
   T visitVariableInitialization(VariableInitialization node) {
     if (node.value != null) {
@@ -205,6 +203,8 @@ abstract class Node {
 
   VariableUse asVariableUse() => null;
 
+  bool get isCommaOperator => false;
+
   Statement toStatement() {
     throw new UnsupportedError('toStatement');
   }
@@ -601,22 +601,6 @@ class VariableDeclarationList extends Expression {
   int get precedenceLevel => EXPRESSION;
 }
 
-class Sequence extends Expression {
-  final List<Expression> expressions;
-
-  Sequence(this.expressions);
-
-  accept(NodeVisitor visitor) => visitor.visitSequence(this);
-
-  void visitChildren(NodeVisitor visitor) {
-    for (Expression expr in expressions) expr.accept(visitor);
-  }
-
-  Sequence _clone() => new Sequence(expressions);
-
-  int get precedenceLevel => EXPRESSION;
-}
-
 class Assignment extends Expression {
   final Expression leftHandSide;
   final String op;         // Null, if the assignment is not compound.
@@ -716,6 +700,8 @@ class Binary extends Expression {
     right.accept(visitor);
   }
 
+  bool get isCommaOperator => op == ',';
+
   int get precedenceLevel {
     // TODO(floitsch): switch to constant map.
     switch (op) {