Split payload application code into a subdirectory.

This patch splits from the main libupdate_engine code the part that
is strictly used to download and apply a payload into a new static
library, moving the code to subdirectories. The new library is divided
in two subdirectories: common/ and payload_consumer/, and should not
depend on other update_engine files outside those two subdirectories.
The main difference between those two is that the common/ tools are more
generic and not tied to the payload consumer process, but otherwise they
are both compiled together.

There are still dependencies from the new libpayload_consumer library
into the main directory files and DBus generated files. Those will be
addressed in follow up CLs.

Bug: 25197634
Test: FEATURES=test emerge-link update_engine; `mm` on Brillo.

Change-Id: Id8d0204ea573627e6e26ca9ea17b9592ca95bc23
diff --git a/payload_consumer/fake_extent_writer.h b/payload_consumer/fake_extent_writer.h
new file mode 100644
index 0000000..762c6d5
--- /dev/null
+++ b/payload_consumer/fake_extent_writer.h
@@ -0,0 +1,71 @@
+//
+// Copyright (C) 2015 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_PAYLOAD_CONSUMER_FAKE_EXTENT_WRITER_H_
+#define UPDATE_ENGINE_PAYLOAD_CONSUMER_FAKE_EXTENT_WRITER_H_
+
+#include <memory>
+#include <vector>
+
+#include <brillo/secure_blob.h>
+
+#include "update_engine/payload_consumer/extent_writer.h"
+
+namespace chromeos_update_engine {
+
+// FakeExtentWriter is a concrete ExtentWriter subclass that keeps track of all
+// the written data, useful for testing.
+class FakeExtentWriter : public ExtentWriter {
+ public:
+  FakeExtentWriter() = default;
+  ~FakeExtentWriter() override = default;
+
+  // ExtentWriter overrides.
+  bool Init(FileDescriptorPtr /* fd */,
+            const std::vector<Extent>& /* extents */,
+            uint32_t /* block_size */) override {
+    init_called_ = true;
+    return true;
+  };
+  bool Write(const void* bytes, size_t count) override {
+    if (!init_called_ || end_called_)
+      return false;
+    written_data_.insert(written_data_.end(),
+                         reinterpret_cast<const uint8_t*>(bytes),
+                         reinterpret_cast<const uint8_t*>(bytes) + count);
+    return true;
+  }
+  bool EndImpl() override {
+    end_called_ = true;
+    return true;
+  }
+
+  // Fake methods.
+  bool InitCalled() { return init_called_; }
+  bool EndCalled() { return end_called_; }
+  brillo::Blob WrittenData() { return written_data_; }
+
+ private:
+  bool init_called_{false};
+  bool end_called_{false};
+  brillo::Blob written_data_;
+
+  DISALLOW_COPY_AND_ASSIGN(FakeExtentWriter);
+};
+
+}  // namespace chromeos_update_engine
+
+#endif  // UPDATE_ENGINE_PAYLOAD_CONSUMER_FAKE_EXTENT_WRITER_H_