Regression test for Utf-8 BOM handling (crbug.com/685618).

test/cctest/parsing/test-scanner-streams.cc

Index: test/cctest/parsing/test-scanner-streams.cc
diff --git a/test/cctest/parsing/test-scanner-streams.cc b/test/cctest/parsing/test-scanner-streams.cc
index 8d84dc8f06cd6224589e4c4f80f85f1a58ce6be3..b4b28f1fc5b67cc07e9f6e29720cd7567a272a07 100644
--- a/test/cctest/parsing/test-scanner-streams.cc
+++ b/test/cctest/parsing/test-scanner-streams.cc
@@ -132,6 +132,13 @@ TEST(Utf8StreamBOM) {
 
   stream->Seek(5);
   CHECK_EQ(unicode_ucs2[5], stream->Advance());
+
+  // Try again, but make sure we have to seek 'backwards'.
+  while (v8::internal::Utf16CharacterStream::kEndOfInput != stream->Advance()) {
+    // Do nothing. We merely advance the stream to the end of its input.
+  }
+  stream->Seek(5);
+  CHECK_EQ(unicode_ucs2[5], stream->Advance());
 }
 
 TEST(Utf8SplitBOM) {