Retrieves android properties from system environment varaibles.

- Converts the key names to capital letters.
- Replaces '.' with '-', as '.' is not supported in env variable names.


diff --git a/platform2/aosp/system/libbase/properties.cpp b/platform2/aosp/system/libbase/properties.cpp
index 8190987..34bd3e4 100644
--- a/platform2/aosp/system/libbase/properties.cpp
+++ b/platform2/aosp/system/libbase/properties.cpp
@@ -20,6 +20,9 @@
 #define _REALLY_INCLUDE_SYS__SYSTEM_PROPERTIES_H_
 #include <sys/system_properties.h>
 #include <sys/_system_properties.h>
+#else
+#include <stdlib.h>
+#include <cstring>
 #endif

 #include <algorithm>
@@ -53,6 +56,23 @@ int __system_property_set(const char* key, const char* value) {
   return 0;
 }

+// Convert a key name to a format acceptible for an envronment variable
+std::string ConvertKeyToEnvVar(const std::string& key) {
+  std::string result = key;
+  // Convert to upper case
+  std::transform(result.begin(), result.end(), result.begin(), ::toupper);
+  // Convert '.' to '_'
+  std::replace(result.begin(), result.end(), '.', '_');
+
+  return result;
+}
+
+std::string GetPropertyFromEnvVar(const std::string& key, const std::string& default_value) {
+  std::string env_key = ConvertKeyToEnvVar(key);
+  char* env_value = getenv(env_key.c_str());
+  return env_value ? std::string(env_value) : default_value;
+}
+
 int __system_property_get(const char* key, char* value) {
   auto it = g_properties.find(key);
   if (it == g_properties.end()) {
@@ -119,10 +139,12 @@ std::string GetProperty(const std::string& key, const std::string& default_value
                                   },
                                   &property_value);
 #else
-  // TODO: implement host __system_property_find()/__system_property_read_callback()?
   auto it = g_properties.find(key);
-  if (it == g_properties.end()) return default_value;
-  property_value = it->second;
+  if (it != g_properties.end()) {
+    property_value = it->second;
+  } else {
+    property_value = GetPropertyFromEnvVar(key, default_value);
+  }
 #endif
   // If the property exists but is empty, also return the default value.
   // Since we can't remove system properties, "empty" is traditionally