Fixing analyzer warnings on overloading == but not get hashCode.

sdk/lib/html/html_common/jenkins_smi_hash.dart

+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+part of html_common;
+
+/**
+ * This is the [Jenkins hash function][1] but using masking to keep
+ * values in SMI range.
+ *
+ * [1]: http://en.wikipedia.org/wiki/Jenkins_hash_function
+ *
+ * Use:
+ * Hash each value with the hash of the previous value, then get the final
+ * hash by calling finish.
+ *
+ *     var hash = 0;
+ *     for (var value in values) {
+ *       hash = JenkinsSmiHash.combine(hash, value.hashCode);
+ *     }
+ *     hash = JenkinsSmiHash.finish(hash);
+ */
+class JenkinsSmiHash {
+  // TODO: Bug 11617- This class should be optimized and standardized elsewhere.
+
+  static int combine(int hash, int value) {
+    hash = 0x1fffffff & (hash + value);
+    hash = 0x1fffffff & (hash + ((0x0007ffff & hash) << 10));
+    return hash ^ (hash >> 6);
+  }
+
+  static int finish(int hash) {
+    hash = 0x1fffffff & (hash + ((0x03ffffff & hash) <<  3));
+    hash = hash ^ (hash >> 11);
+    return 0x1fffffff & (hash + ((0x00003fff & hash) << 15));
+  }
+
+  static int hash2(a, b) => finish(combine(combine(0, a), b));
+
+  static int hash4(a, b, c, d) =>
+      finish(combine(combine(combine(combine(0, a), b), c), d));
+}