Make scanner not accept invalid unicode escapes in identifiers.

test/mjsunit/regress/regress-1620.js

Index: test/mjsunit/regress/regress-1620.js
diff --git a/test/mjsunit/regress/regress-1620.js b/test/mjsunit/regress/regress-1620.js
new file mode 100644
index 0000000000000000000000000000000000000000..8deed1e9233c0f43f5ea40ee80c9b623a4349267
--- /dev/null
+++ b/test/mjsunit/regress/regress-1620.js
@@ -0,0 +1,35 @@
+// Copyright 2011 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// See: http://code.google.com/p/v8/issues/detail?id=1620
+
+assertThrows("var \\u\\u\\u = 42;");
+assertThrows("var \\u41 = 42;");
+assertThrows("var \\u123 = 42;");
+eval("var \\u1234 = 42;");
+assertEquals(42, eval("\u1234"));
+assertThrows("var uuu = 42; var x = \\u\\u\\u");