DO NOT MERGE: Resolve mBehindAlpha with mCurrentBehindAlpha

fixes a build breakage, mBehindAlpha is a master thing but mCurrentBehindAlpha is a QPR1 thing

BUG: 151041066
Test: Compile
Change-Id: I78d767319d2ba856a9f453f71b39ddd3c96e6b9f

packages/SystemUI/src/com/android/systemui/statusbar/phone/ScrimController.java

@@ -473,9 +473,9 @@ public class ScrimController implements ViewTreeObserver.OnPreDrawListener, OnCo
             mCurrentBehindTint = ColorUtils.blendARGB(ScrimState.BOUNCER.getBehindTint(),
                     mState.getBehindTint(), interpolatedFract);
         }
-        if (isNaN(mBehindAlpha) || isNaN(mInFrontAlpha)) {
+        if (isNaN(mCurrentBehindAlpha) || isNaN(mCurrentInFrontAlpha)) {
             throw new IllegalStateException("Scrim opacity is NaN for state: " + mState
-                    + ", front: " + mInFrontAlpha + ", back: " + mBehindAlpha);
+                    + ", front: " + mCurrentInFrontAlpha + ", back: " + mCurrentBehindAlpha);
         }
     }