Keep PhoneStatusBar default constructor around.

By keeping the entire class safe.

Change-Id: I0851ae5556243af2deb76f38500271059ffa4480
diff --git a/packages/SystemUI/proguard.flags b/packages/SystemUI/proguard.flags
index ab45d99..1ff93d2 100644
--- a/packages/SystemUI/proguard.flags
+++ b/packages/SystemUI/proguard.flags
@@ -7,4 +7,5 @@
   public void setGlowScale(float);
 }
 
+-keep class com.android.systemui.statusbar.phone.PhoneStatusBar
 -keep class com.android.systemui.statusbar.tv.TvStatusBar