Add preferences to the list of not proguarded classes.

Change-Id: Ib7db435bb640b3a3feaa0534ccc77b6f9eda0800
diff --git a/changes.txt b/changes.txt
index 9bc8a66..1601ec7 100644
--- a/changes.txt
+++ b/changes.txt
@@ -1,5 +1,10 @@
 Change log for Android SDK Tools.
 
+Revision 9:
+- Default proguard config file changes:
+   * ignore classes extending android.preference.Preference
+   * ignore classes extending android.app.backup.BackupAgentHelper
+
 Revision 8:
 - New SDK component: platform-tools. This makes all platforms use the same
   latest version of aapt/aidl/dx.
diff --git a/files/proguard.cfg b/files/proguard.cfg
index a88f3b7..12dd039 100644
--- a/files/proguard.cfg
+++ b/files/proguard.cfg
@@ -11,6 +11,7 @@
 -keep public class * extends android.content.BroadcastReceiver
 -keep public class * extends android.content.ContentProvider
 -keep public class * extends android.app.backup.BackupAgentHelper
+-keep public class * extends android.preference.Preference
 -keep public class com.android.vending.licensing.ILicensingService
 
 -keepclasseswithmembernames class * {