Calling buildLayer only on views which are actually visible

> Creating a common listener for handling buildLayer logic

Bug: 30138067
Change-Id: I803ef78b48e07e5ae5922e0392d390f274a87d75

src/com/android/launcher3/anim/AnimationLayerSet.java

@@ -0,0 +1,53 @@
+/*
+ * Copyright (C) 2016 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.anim;
+
+import android.animation.Animator;
+import android.animation.AnimatorListenerAdapter;
+import android.view.View;
+
+import java.util.HashSet;
+
+/**
+ * Helper class to automatically build view hardware layers for the duration of an animation.
+ */
+public class AnimationLayerSet extends AnimatorListenerAdapter {
+
+    private final HashSet<View> mViews = new HashSet<>();
+
+    public void addView(View v) {
+        mViews.add(v);
+    }
+
+    @Override
+    public void onAnimationStart(Animator animation) {
+        // Enable all necessary layers
+        for (View v : mViews) {
+            v.setLayerType(View.LAYER_TYPE_HARDWARE, null);
+            if (v.isAttachedToWindow() && v.getVisibility() == View.VISIBLE) {
+                v.buildLayer();
+            }
+        }
+    }
+
+    @Override
+    public void onAnimationEnd(Animator animation) {
+        for (View v : mViews) {
+            v.setLayerType(View.LAYER_TYPE_NONE, null);
+        }
+    }
+}