Add JavaScript AST.

lib/compiler/implementation/js/precedence.dart

Index: lib/compiler/implementation/js/precedence.dart
diff --git a/lib/compiler/implementation/js/precedence.dart b/lib/compiler/implementation/js/precedence.dart
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+// Copyright (c) 2012, 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.
+
+#library("precedence");
+
+final EXPRESSION = 0;
+final ASSIGNMENT = EXPRESSION + 1;
+final LOGICAL_OR = ASSIGNMENT + 1;
+final LOGICAL_AND = LOGICAL_OR + 1;
+final BIT_OR = LOGICAL_AND + 1;
+final BIT_XOR = BIT_OR + 1;
+final BIT_AND = BIT_XOR + 1;
+final EQUALITY = BIT_AND + 1;
+final RELATIONAL = EQUALITY + 1;
+final SHIFT = RELATIONAL + 1;
+final ADDITIVE = SHIFT + 1;
+final MULTIPLICATIVE = ADDITIVE + 1;
+final UNARY = MULTIPLICATIVE + 1;
+final LEFT_HAND_SIDE = UNARY + 1;
+// We merge new, call and member expressions.
+// This means that we have to emit parenthesis for 'new's. For example `new X;`
+// should be printed as `new X();`. This simplifies the requirements.
+final CALL = LEFT_HAND_SIDE;
+final PRIMARY = CALL + 1;