Add PowerUsageSummary to proguard list.

Bug: 4975279
Change-Id: I8e36dd6ce6f0e6a7859af00e7980e636933140fb
diff --git a/proguard.flags b/proguard.flags
index 8318101..6d41d17 100644
--- a/proguard.flags
+++ b/proguard.flags
@@ -10,4 +10,5 @@
 -keep class com.android.settings.MasterClear
 -keep class com.android.settings.MasterClearConfirm
 -keep class com.android.settings.accounts.*
+-keep class com.android.settings.fuelgauge.*