Improve debugging setup for window manager package.

This moves debug flags to a dedicated class and also provides a
mechanism to either have fine grained tags or one common tag for easier
grepping the logcat. This mimicks the approach in activity manager
package.

Change-Id: Ie8c08b9a3d8b182335ee5547ee05d21b5933db6b
diff --git a/services/core/java/com/android/server/wm/DockedStackDividerController.java b/services/core/java/com/android/server/wm/DockedStackDividerController.java
index 32c9b2a..8f3d3e3 100644
--- a/services/core/java/com/android/server/wm/DockedStackDividerController.java
+++ b/services/core/java/com/android/server/wm/DockedStackDividerController.java
@@ -27,13 +27,15 @@
 import static android.view.WindowManager.DOCKED_LEFT;
 import static android.view.WindowManager.DOCKED_RIGHT;
 import static android.view.WindowManager.DOCKED_TOP;
+import static com.android.server.wm.WindowManagerDebugConfig.TAG_WITH_CLASS_NAME;
+import static com.android.server.wm.WindowManagerDebugConfig.TAG_WM;
 
 /**
  * Keeps information about the docked stack divider.
  */
 public class DockedStackDividerController {
 
-    private static final String TAG = "DockedStackDividerController";
+    private static final String TAG = TAG_WITH_CLASS_NAME ? "DockedStackDividerController" : TAG_WM;
 
     private final DisplayContent mDisplayContent;
     private final int mDividerWindowWidth;