Implemented automatic caching for the discovery documents.
diff --git a/googleapiclient/discovery_cache/base.py b/googleapiclient/discovery_cache/base.py
new file mode 100644
index 0000000..00e466d
--- /dev/null
+++ b/googleapiclient/discovery_cache/base.py
@@ -0,0 +1,45 @@
+# Copyright 2014 Google Inc. All Rights Reserved.
+#
+# 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.
+
+"""An abstract class for caching the discovery document."""
+
+import abc
+
+
+class Cache(object):
+  """A base abstract cache class."""
+  __metaclass__ = abc.ABCMeta
+
+  @abc.abstractmethod
+  def get(self, url):
+    """Gets the content from the memcache with a given key.
+
+    Args:
+      url: string, the key for the cache.
+
+    Returns:
+      object, the value in the cache for the given key, or None if the key is
+      not in the cache.
+    """
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def set(self, url, content):
+    """Sets the given key and content in the cache.
+
+    Args:
+      url: string, the key for the cache.
+      content: string, the discovery document.
+    """
+    raise NotImplementedError()