Refactor keys and queries in datastore service and implementation.

service/datastore/testable.go

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package datastore
 
-type TestingSnapshot interface{}
+// TestingSnapshot is an opaque implementation-defined snapshot type.
+type TestingSnapshot interface {
+        ImATestingSnapshot()
+}
 
 // Testable is the testable interface for fake datastore implementations.
 type Testable interface {
         // AddIndex adds the provided index.
         // Blocks all datastore access while the index is built.
         // Panics if any of the IndexDefinition objects are not Compound()
         AddIndexes(...*IndexDefinition)
 
         // TakeIndexSnapshot allows you to take a snapshot of the current index
         // tables, which can be used later with SetIndexSnapshot.
@@ skipping 14 matching lines @@
         //
         // But depending on the implementation it may implemented with an atomic
         // operation.
         CatchupIndexes()
 
         // SetTransactionRetryCount set how many times RunInTransaction will retry
         // transaction body pretending transaction conflicts happens. 0 (default)
         // means commit succeeds on the first attempt (no retries).
         SetTransactionRetryCount(int)
 }