update_engine: Rename "chromeos" -> "brillo" in include paths and namespaces

libchromeos is transitioning to libbrillo and chromeos namespaces
and include directory is changing to brillo.

Bug: 24872993
Change-Id: I770659a95be380a50fe3b2ba9f91d65818f40945
diff --git a/payload_generator/fake_filesystem.h b/payload_generator/fake_filesystem.h
index 095f8a8..a14b8d3 100644
--- a/payload_generator/fake_filesystem.h
+++ b/payload_generator/fake_filesystem.h
@@ -38,7 +38,7 @@
   size_t GetBlockSize() const override;
   size_t GetBlockCount() const override;
   bool GetFiles(std::vector<File>* files) const override;
-  bool LoadSettings(chromeos::KeyValueStore* store) const override;
+  bool LoadSettings(brillo::KeyValueStore* store) const override;
 
   // Fake methods.