Code to enable dragging to System UI shelf.

This CL doesn’t let the new code run, it’s under a compile-time flag,
and the behavior should be same as before.

The change introduces a concept of a DragDriver, which encapsulates
behavior of the existing DND (InternalDragDriver) or the framework-
driven DND (SystemDragDriver).

An instance of DragDriver gets created by DragController for the time
while a DND operation is in progress, and it takes care of translating
DND events for DragController.

Also did some cleanups, like removing meaningless fields etc.

Plans for future: keep working in Burnaby, and:
* Perhaps, better separate DragDriver from DragController
* Detect fling gesture for system DND
* Look at accessibility
* Polish animations and appearance
* Fix dragging from folders
* Support cancelling DND

Then, it will become possible to enable new dragging (based on Android
version).

Bug: 22028725
Change-Id: I41b40e9d512d83937f5b101ac8e3e8e7e807c269

src/com/android/launcher3/AnotherWindowDropTarget.java

@@ -0,0 +1,73 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.launcher3;
+
+import android.content.Context;
+import android.graphics.PointF;
+import android.graphics.Rect;
+
+/**
+ * Drop target used when another window (i.e. another process) has accepted a global system drag.
+ * If the accepted item was a shortcut, we delete it from Launcher.
+ */
+public class AnotherWindowDropTarget implements DropTarget {
+    final Launcher mLauncher;
+
+    AnotherWindowDropTarget (Context context) { mLauncher = (Launcher) context; }
+
+    @Override
+    public boolean isDropEnabled() { return true; }
+
+    @Override
+    public void onDrop(DragObject dragObject) {
+        dragObject.deferDragViewCleanupPostAnimation = false;
+        LauncherModel.deleteItemFromDatabase(mLauncher, (ShortcutInfo) dragObject.dragInfo);
+    }
+
+    @Override
+    public void onDragEnter(DragObject dragObject) {}
+
+    @Override
+    public void onDragOver(DragObject dragObject) {}
+
+    @Override
+    public void onDragExit(DragObject dragObject) {}
+
+    @Override
+    public void onFlingToDelete(DragObject dragObject, PointF vec) {}
+
+    @Override
+    public boolean acceptDrop(DragObject dragObject) {
+        return dragObject.dragInfo instanceof ShortcutInfo;
+    }
+
+    @Override
+    public void prepareAccessibilityDrop() {}
+
+    // These methods are implemented in Views
+    @Override
+    public void getHitRectRelativeToDragLayer(Rect outRect) {}
+
+    @Override
+    public void getLocationInDragLayer(int[] loc) {}
+
+    @Override
+    public int getLeft() { return 0; }
+
+    @Override
+    public int getTop() { return 0; }
+}