Add icon recents view for Go

Add a specific view for Go's icon recents. We also add a few properties
for use in future refactors.

Bug: 114136250
Test: Build Launcher3GoIconRecents
Change-Id: I9852679256158344ab276d1c477f55b7dd2d6a52

go/quickstep/res/layout/icon_recents_root_view.xml

@@ -14,11 +14,17 @@
      See the License for the specific language governing permissions and
      limitations under the License.
 -->
-<!-- TODO(114136250): Remove this temporary placeholder view for Go recents -->
-<TextView
+<com.android.quickstep.views.IconRecentsView
     xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
-    android:gravity="center"
-    android:text="Stub!"
-    android:textSize="40sp"/>
+    android:gravity="center">
+    <!-- TODO(114136250): Remove this temporary placeholder view for Go recents -->
+    <TextView
+        xmlns:android="http://schemas.android.com/apk/res/android"
+        android:layout_width="match_parent"
+        android:layout_height="match_parent"
+        android:gravity="center"
+        android:text="Stub!"
+        android:textSize="40sp"/>
+</com.android.quickstep.views.IconRecentsView>

go/quickstep/src/com/android/quickstep/views/IconRecentsView.java

@@ -0,0 +1,75 @@
+/*
+ * Copyright (C) 2019 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.quickstep.views;
+
+import android.content.Context;
+import android.util.AttributeSet;
+import android.util.FloatProperty;
+import android.view.ViewDebug;
+import android.widget.FrameLayout;
+
+/**
+ * Root view for the icon recents view.
+ */
+public final class IconRecentsView extends FrameLayout {
+
+    public static final FloatProperty<IconRecentsView> TRANSLATION_Y_FACTOR =
+            new FloatProperty<IconRecentsView>("translationYFactor") {
+
+                @Override
+                public void setValue(IconRecentsView view, float v) {
+                    view.setTranslationYFactor(v);
+                }
+
+                @Override
+                public Float get(IconRecentsView view) {
+                    return view.mTranslationYFactor;
+                }
+            };
+
+    public static final FloatProperty<IconRecentsView> CONTENT_ALPHA =
+            new FloatProperty<IconRecentsView>("contentAlpha") {
+                @Override
+                public void setValue(IconRecentsView view, float v) {
+                    ALPHA.set(view, v);
+                }
+
+                @Override
+                public Float get(IconRecentsView view) {
+                    return ALPHA.get(view);
+                }
+            };
+
+    /**
+     * A ratio representing the view's relative placement within its padded space. For example, 0
+     * is top aligned and 0.5 is centered vertically.
+     */
+    @ViewDebug.ExportedProperty(category = "launcher")
+    private float mTranslationYFactor;
+
+    public IconRecentsView(Context context, AttributeSet attrs) {
+        super(context, attrs);
+    }
+
+    public void setTranslationYFactor(float translationFactor) {
+        mTranslationYFactor = translationFactor;
+        setTranslationY(computeTranslationYForFactor(mTranslationYFactor));
+    }
+
+    private float computeTranslationYForFactor(float translationYFactor) {
+        return translationYFactor * (getPaddingBottom() - getPaddingTop());
+    }
+}

quickstep/src/com/android/quickstep/views/LauncherRecentsView.java

@@ -67,6 +67,10 @@ public class LauncherRecentsView extends RecentsView<Launcher> {
                 }
             };
 
+    /**
+     * A ratio representing the view's relative placement within its padded space. For example, 0
+     * is top aligned and 0.5 is centered vertically.
+     */
     @ViewDebug.ExportedProperty(category = "launcher")
     private float mTranslationYFactor;