Beginning of CSS parser using frog parsering infrastructure.

frog/source.dart

Index: frog/source.dart
diff --git a/frog/source.dart b/frog/source.dart
index 1ff314485322c8c6ff8fce4253d504e9c1d1d7ad..ab62a2fe3a43592c14adba3e54dc23484e70d16c 100644
--- a/frog/source.dart
+++ b/frog/source.dart
@@ -7,6 +7,10 @@
  * Represents a file of source code.
  */
 class SourceFile implements Comparable {
+  // TODO(terry): This filename for in memory buffer.  May need to rework if
+  //              filename is used for more than informational.
+  static String IN_MEMORY_FILE = '<buffer>';
+
   /** The name of the file. */
   final String filename;