Fix alpha animation bug in keyguard

The setters/getters were being stripped by proguard, resulting
in janky transitions in keyguard alpha animations.

Change-Id: Ifd4574d9b64eb2b038acac41bfc8418745ee12a2

packages/Keyguard/proguard.flags

@@ -1,2 +1,27 @@
--keep public class com.android.keyguard.KeyguardService
+-keep public class * {
+  public void setBackgroundAlpha(float);
+  public float getBackgroundAlpha();
+  public void setContentAlpha(float);
+  public float getContentAlpha();
+  public void setAlpha(float);
+  public float getAlpha();
+  public void setAlpha(int);
+  public int getAlpha();
+  public void setRotationX(float);
+  public float getRotationX();
+  public void setRotationY(float);
+  public float getRotationY();
+  public void setPivotX(float);
+  public float getPivotX();
+  public void setPivotY(float);
+  public float getPivotY();
+  public void setScaleX(float);
+  public float getScaleX();
+  public void setScaleY(float);
+  public float getScaleY();
+  public void setTranslationX(float);
+  public float getTranslationX();
+  public void setTranslationY(float);
+  public float getTranslationY();
+}