App Pairs: Implement save, inflate, launch, and delete

This is the third of several patches implementing the App Pairs feature behind a flag.

This patch includes:
- AppPairIcon and associated XML. Actual icon asset is placeholder for now
- Ability to launch split pair on click
- Icon can be moved around, incl. to Taskbar
- App pair can be deleted by dragging to "Remove" drop zone
- Icon persists on Launcher reload

Change-Id: I88aec6fbc814be98f9ef048bbc5af889d0797970
Flag: ENABLE_APP_PAIRS (set to false)
Bug: 274835596
Test: Not included in this CL, but will follow

src/com/android/launcher3/touch/ItemClickHandler.java

@@ -42,6 +42,7 @@ import com.android.launcher3.Launcher;
 import com.android.launcher3.LauncherSettings;
 import com.android.launcher3.R;
 import com.android.launcher3.Utilities;
+import com.android.launcher3.apppairs.AppPairIcon;
 import com.android.launcher3.folder.Folder;
 import com.android.launcher3.folder.FolderIcon;
 import com.android.launcher3.logging.InstanceId;
@@ -95,6 +96,8 @@ public class ItemClickHandler {
         } else if (tag instanceof FolderInfo) {
             if (v instanceof FolderIcon) {
                 onClickFolderIcon(v);
+            } else if (v instanceof AppPairIcon) {
+                onClickAppPairIcon(v);
             }
         } else if (tag instanceof AppInfo) {
             startAppShortcutOrInfoActivity(v, (AppInfo) tag, launcher);
@@ -122,6 +125,17 @@ public class ItemClickHandler {
         }
     }
 
+    /**
+     * Event handler for an app pair icon click.
+     *
+     * @param v The view that was clicked. Must be an instance of {@link AppPairIcon}.
+     */
+    private static void onClickAppPairIcon(View v) {
+        Launcher launcher = Launcher.getLauncher(v.getContext());
+        FolderInfo folderInfo = ((AppPairIcon) v).getInfo();
+        launcher.launchAppPair(folderInfo.contents.get(0), folderInfo.contents.get(1));
+    }
+
     /**
      * Event handler for the app widget view which has not fully restored.
      */