Accept raw strings prefixed by 'r' (issue 4815)

compiler/java/com/google/dart/compiler/parser/DartScanner.java

Index: compiler/java/com/google/dart/compiler/parser/DartScanner.java
===================================================================
--- compiler/java/com/google/dart/compiler/parser/DartScanner.java	(revision 12197)
+++ compiler/java/com/google/dart/compiler/parser/DartScanner.java	(working copy)
@@ -1214,6 +1214,13 @@
       case '#':
         return scanDirective();
 
+      case 'r':
+        if (lookahead(1) == '\'' || lookahead(1) == '"') {
+          advance();
+          return scanString(true);
+        }
+        return scanIdentifier(true);
+
       default:
         if (isIdentifierStart(lookahead(0))) {
           boolean allowDollars = true;