Create an abstract Manifest base class

This will help as we add support for another manifest type.

Signed-off-by: Shawn O. Pearce <sop@google.com>

manifest_loader.py

@@ -0,0 +1,27 @@
+#
+# Copyright (C) 2009 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from manifest_xml import XmlManifest
+
+def ParseManifest(repodir):
+  return XmlManifest(repodir)
+
+_manifest = None
+
+def GetManifest(repodir, reparse=False):
+  global _manifest
+  if _manifest is None or reparse:
+    _manifest = ParseManifest(repodir)
+  return _manifest