Nested comments.

dart/frog/leg/scanner/scanner.dart

Index: dart/frog/leg/scanner/scanner.dart
diff --git a/dart/frog/leg/scanner/scanner.dart b/dart/frog/leg/scanner/scanner.dart
index e0e85d72c60dbecca39fd878a91f6de5c1459501..bfce2342cb9597ab318b32124ef838c973f29a26 100644
--- a/dart/frog/leg/scanner/scanner.dart
+++ b/dart/frog/leg/scanner/scanner.dart
@@ -518,16 +518,27 @@ class AbstractScanner<T> implements Scanner {
   }
 
   int tokenizeMultiLineComment(int next) {
+    int nesting = 1;
     next = advance();
     while (true) {
       if ($EOF === next) {
+        // TODO(ahe): Report error.
         return next;
       } else if ($STAR === next) {
         next = advance();
-        if (next === $SLASH) {
-          return advance();
-        } else if (next === $EOF) {
-          return next;
+        if ($SLASH === next) {
+          --nesting;
+          if (0 === nesting) {
+            return advance();
+          } else {
+            next = advance();
+          }
+        }
+      } else if ($SLASH === next) {
+        next = advance();
+        if ($STAR === next) {
+          next = advance();
+          ++nesting;
         }
       } else {
         next = advance();