Don't apply dim if there is no docked stack

Also add proper names for the different dim layer surfaces, so we
better know where they are coming from when we see it in the
surface flinger dump.

Bug: 27270126
Bug: 27200491
Change-Id: Ic085e8505d20a941f4631ec914f00eefda74a766
diff --git a/services/core/java/com/android/server/wm/TaskPositioner.java b/services/core/java/com/android/server/wm/TaskPositioner.java
index f7035c5..92701de 100644
--- a/services/core/java/com/android/server/wm/TaskPositioner.java
+++ b/services/core/java/com/android/server/wm/TaskPositioner.java
@@ -60,7 +60,8 @@
 import java.lang.annotation.RetentionPolicy;
 
 class TaskPositioner implements DimLayer.DimLayerUser {
-    private static final String TAG = TAG_WITH_CLASS_NAME ? "TaskPositioner" : TAG_WM;
+    private static final String TAG_LOCAL = "TaskPositioner";
+    private static final String TAG = TAG_WITH_CLASS_NAME ? TAG_LOCAL : TAG_WM;
 
     // The margin the pointer position has to be within the side of the screen to be
     // considered at the side of the screen.
@@ -287,7 +288,7 @@
         }
         mService.pauseRotationLocked();
 
-        mDimLayer = new DimLayer(mService, this, mDisplay.getDisplayId());
+        mDimLayer = new DimLayer(mService, this, mDisplay.getDisplayId(), TAG_LOCAL);
         mSideMargin = dipToPixel(SIDE_MARGIN_DIP, mDisplayMetrics);
         mMinVisibleWidth = dipToPixel(MINIMUM_VISIBLE_WIDTH_IN_DP, mDisplayMetrics);
         mMinVisibleHeight = dipToPixel(MINIMUM_VISIBLE_HEIGHT_IN_DP, mDisplayMetrics);