Remove js.Sequence and use binary comma operator instead.

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

Index: sdk/lib/_internal/compiler/implementation/js/printer.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js/printer.dart b/sdk/lib/_internal/compiler/implementation/js/printer.dart
index 38c9449ba582b223acdaea8a1b7fd30d72c46322..6d663bc5b99bdd16a89a34b4576bb7ed8bc2be56 100644
--- a/sdk/lib/_internal/compiler/implementation/js/printer.dart
+++ b/sdk/lib/_internal/compiler/implementation/js/printer.dart
@@ -481,15 +481,6 @@ class Printer implements NodeVisitor {
                         newInForInit: inForInit, newAtStatementBegin: false);
   }
 
-  visitSequence(Sequence sequence) {
-    // Note that we only require that the entries are expressions and not
-    // assignments. This means that nested sequences are not put into
-    // parenthesis.
-    visitCommaSeparated(sequence.expressions, EXPRESSION,
-                        newInForInit: false,
-                        newAtStatementBegin: atStatementBegin);
-  }
-
   visitAssignment(Assignment assignment) {
     visitNestedExpression(assignment.leftHandSide, LEFT_HAND_SIDE,
                           newInForInit: inForInit,
@@ -556,8 +547,9 @@ class Printer implements NodeVisitor {
     bool leftSpace = true;   // left<HERE>op right
     switch (op) {
       case ',':
+        //  x, (y, z) <=> (x, y), z.
         leftPrecedenceRequirement = EXPRESSION;
-        rightPrecedenceRequirement = LOGICAL_OR;
+        rightPrecedenceRequirement = EXPRESSION;
         leftSpace = false;
         break;
       case "||":