update_engine: Implement Excluder Class + Tests

Excluder persists the exclusion state for excluding certain names. This
will be used to exclude update Payloads which are contiuously faulty.

BUG=chromium:928805
TEST=FEATURES=test emerge-$B update_engine
TEST=USE="${USE} -dlc" FEATURES=test emerge-$B update_engine

Change-Id: I780a9cf2ad979833382a832e01833211ec2ccf7d
Reviewed-on: https://chromium-review.googlesource.com/c/aosp/platform/system/update_engine/+/2172074
Tested-by: Jae Hoon Kim <kimjae@chromium.org>
Commit-Queue: Jae Hoon Kim <kimjae@chromium.org>
Auto-Submit: Jae Hoon Kim <kimjae@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
diff --git a/common/excluder_stub.h b/common/excluder_stub.h
new file mode 100644
index 0000000..2d5372a
--- /dev/null
+++ b/common/excluder_stub.h
@@ -0,0 +1,46 @@
+//
+// Copyright (C) 2020 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.
+//
+
+#ifndef UPDATE_ENGINE_COMMON_EXCLUDER_STUB_H_
+#define UPDATE_ENGINE_COMMON_EXCLUDER_STUB_H_
+
+#include <string>
+
+#include "update_engine/common/excluder_interface.h"
+
+namespace chromeos_update_engine {
+
+// An implementation of the |ExcluderInterface| that does nothing.
+class ExcluderStub : public ExcluderInterface {
+ public:
+  ExcluderStub() = default;
+  ~ExcluderStub() = default;
+
+  // |ExcluderInterface| overrides.
+  bool Exclude(const std::string& name) override;
+  bool IsExcluded(const std::string& name) override;
+  bool Reset() override;
+
+  // Not copyable or movable.
+  ExcluderStub(const ExcluderStub&) = delete;
+  ExcluderStub& operator=(const ExcluderStub&) = delete;
+  ExcluderStub(ExcluderStub&&) = delete;
+  ExcluderStub& operator=(ExcluderStub&&) = delete;
+};
+
+}  // namespace chromeos_update_engine
+
+#endif  // UPDATE_ENGINE_COMMON_EXCLUDER_STUB_H_