Pass charset to XmlPullParser.setInput instead of null

Passing null to XmlPullParser.setInput forces it to do additional
work, which can be easily avoided if we know the charset beforehand.

bug: b/20849543

Change-Id: Iaff97be9df2d0f99d7af8f19f65934439c9658e2
diff --git a/services/core/java/com/android/server/DeviceIdleController.java b/services/core/java/com/android/server/DeviceIdleController.java
index 5dbf4c9..9b7b2d3 100644
--- a/services/core/java/com/android/server/DeviceIdleController.java
+++ b/services/core/java/com/android/server/DeviceIdleController.java
@@ -71,6 +71,7 @@
 import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.PrintWriter;
+import java.nio.charset.StandardCharsets;
 
 /**
  * Keeps track of device idleness and drives low power mode based on that.
@@ -679,7 +680,7 @@
         }
         try {
             XmlPullParser parser = Xml.newPullParser();
-            parser.setInput(stream, null);
+            parser.setInput(stream, StandardCharsets.UTF_8.name());
             readConfigFileLocked(parser);
         } catch (XmlPullParserException e) {
         } finally {
@@ -756,7 +757,7 @@
         try {
             synchronized (this) {
                 XmlSerializer out = new FastXmlSerializer();
-                out.setOutput(memStream, "utf-8");
+                out.setOutput(memStream, StandardCharsets.UTF_8.name());
                 writeConfigFileLocked(out);
             }
         } catch (IOException e) {