Allow whitespace and \ before the first newline of multiline string.

sdk/lib/_internal/compiler/implementation/dart_backend/dart_printer.dart

 // Copyright (c) 2014, 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.
 
 // TODO(asgerf): Include metadata.
 // TODO(asgerf): Include cascade operator.
 library dart_printer;
 
 import '../dart2jslib.dart' as dart2js;
 import '../tree/tree.dart' as tree;
@@ skipping 1221 matching lines @@
 
   void writeType(TypeAnnotation type) {
     write(type.name);
     if (type.typeArguments != null && type.typeArguments.length > 0) {
       write('<');
       writeEach(',', type.typeArguments, writeType);
       write('>');
     }
   }
 
+  /// A list of string quotings that the printer may use to quote strings.
+  // Ignore multiline quotings for now. Would need to make sure that no
+  // newline (potentially prefixed by whitespace) follows the quoting.
+  // TODO(asgerf): Include multiline quotation schemes.
+  static const _QUOTINGS = const <tree.StringQuoting>[
+      const tree.StringQuoting(characters.$DQ, raw: false, leftQuoteLength: 1),
+      const tree.StringQuoting(characters.$DQ, raw: true, leftQuoteLength: 1),
+      const tree.StringQuoting(characters.$SQ, raw: false, leftQuoteLength: 1),
+      const tree.StringQuoting(characters.$SQ, raw: true, leftQuoteLength: 1),
+  ];
+
   static StringLiteralOutput analyzeStringLiteral(Expression node) {
     // TODO(asgerf): This might be a bit too expensive. Benchmark.
     // Flatten the StringConcat tree.
     List parts = []; // Expression or int (char node)
     void collectParts(Expression e) {
       if (e is StringConcat) {
         e.expressions.forEach(collectParts);
       } else if (e is Literal && e.value is dart2js.StringConstant) {
         for (int char in e.value.value) {
           parts.add(char);
@@ skipping 22 matching lines @@
       return quot.leftQuoteLength + quot.rightQuoteLength;
     }
 
     // Create initial scores for each StringQuoting and index them
     // into raw/non-raw and single-quote/double-quote.
     List<OpenStringChunk> best = <OpenStringChunk>[];
     List<int> raws = <int>[];
     List<int> nonRaws = <int>[];
     List<int> sqs = <int>[];
     List<int> dqs = <int>[];
-    for (tree.StringQuoting q in tree.StringQuoting.mapping) {
-      // Ignore multiline quotings for now. Encoding of line breaks is unclear.
-      // TODO(asgerf): Include multiline quotation schemes.
-      if (q.leftQuoteCharCount >= 3)
-        continue;
+    for (tree.StringQuoting q in _QUOTINGS) {
       OpenStringChunk chunk = new OpenStringChunk(null, q, getQuoteCost(q));
       int index = best.length;
       best.add(chunk);
 
       if (q.raw) {
         raws.add(index);
       } else {
         nonRaws.add(index);
       }
       if (q.quote == characters.$SQ) {
@@ skipping 195 matching lines @@
   final StringChunk previous;
   final tree.StringQuoting quoting;
   num cost;
 
   OpenStringChunk(this.previous, this.quoting, this.cost);
 
   StringChunk end(int endIndex) {
     return new StringChunk(previous, quoting, endIndex);
   }
 }