Made multiline string literals ignore an initial newline.

frog/leg/scanner/byte_strings.dart

Index: frog/leg/scanner/byte_strings.dart
diff --git a/frog/leg/scanner/byte_strings.dart b/frog/leg/scanner/byte_strings.dart
index 8cbe6a9085ef4dea60f6e470c245a8d08a41b531..17777fcafd5fa9e4e4cf79f0407b159d5f670fe0 100644
--- a/frog/leg/scanner/byte_strings.dart
+++ b/frog/leg/scanner/byte_strings.dart
@@ -109,27 +109,17 @@ class Utf8String extends ByteString {
   Iterator<int> iterator() => new Utf8Decoder(bytes, 0, length);
 
   SourceString copyWithoutQuotes(int initial, int terminal) {
-    assert(0 <= initial && initial <= 4);
-    assert(initial !== 1 || bytes[offset] === $SQ ||
-                            bytes[offset] === $DQ);
-    assert(initial !== 2 || (bytes[offset] === $AT &&
-                             (bytes[offset + 1] === $SQ ||
-                              bytes[offset + 1] === $DQ)));
-    assert(initial !== 3 || ((bytes[offset] === $SQ ||
-                              bytes[offset] === $DQ) &&
-                             bytes[offset] === bytes[offset + 1] &&
-                             bytes[offset] === bytes[offset + 2]));
-    assert(initial !== 4 || (bytes[offset] === $AT &&
-                             (bytes[offset + 1] === $SQ ||
-                              bytes[offset + 1] === $DQ) &&
-                              bytes[offset + 2] === bytes[offset + 1] &&
-                              bytes[offset + 3] === bytes[offset + 1]));
-    assert(terminal === 0 || terminal === 1 || terminal === 3);
-    assert(terminal === 0 || ((bytes[end - 1] == $AT ||
-                               bytes[end - 1] === $DQ) &&
-                               (terminal === 1 ||
-                                bytes[end - 2] === bytes[end - 1] &&
-                                bytes[end - 3] === bytes[end - 1])));
+    assert((){
+      // Only allow dropping ASCII characters, to guarantee that
+      // the resulting Utf8String is still valid.
+      for (int i = 0; i < initial; i++) {
+        if (bytes[offset + i] >= 0x80) return false;
+      }
+      for (int i = 0; i < terminal; i++) {
+        if (bytes[offset + length - terminal + i] >= 0x80) return false;
+      }
+      return true;
+    });
     // TODO(lrn): Check that first and last bytes use the same type of quotes.
     return new Utf8String(bytes, offset + initial,
                           length - initial - terminal);