Add PropertyFetcher.

This is a mockable / replacable class for getting sysprops.
On host, sysprops may be provided via ADB or command line
arguments.
On device, default behavior is to use android-base/properties.h.

Bug: 72722951
Test: libvintf_test
Test: vintf_object_test

Change-Id: I752c4336dacd4c5f3254f32e4caf8dc743c636d9
Merged-In: I752c4336dacd4c5f3254f32e4caf8dc743c636d9
diff --git a/utils-common.cpp b/utils-common.cpp
new file mode 100644
index 0000000..3e7e736
--- /dev/null
+++ b/utils-common.cpp
@@ -0,0 +1,42 @@
+
+/*
+ * Copyright (C) 2017 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.
+ */
+
+#include "utils.h"
+
+// Default implementations for classes defined in utils.h
+
+namespace android {
+namespace vintf {
+namespace details {
+
+std::string PropertyFetcher::getProperty(const std::string&,
+                                         const std::string& defaultValue) const {
+    return defaultValue;
+}
+
+uint64_t PropertyFetcher::getUintProperty(const std::string&, uint64_t,
+                                          uint64_t defaultValue) const {
+    return defaultValue;
+}
+
+bool PropertyFetcher::getBoolProperty(const std::string&, bool defaultValue) const {
+    return defaultValue;
+}
+
+}  // namespace details
+}  // namespace vintf
+}  // namespace android