[Download Home] Pull out DeletedFileTracker from DownloadHistoryAdapter

chrome/android/java/src/org/chromium/chrome/browser/download/ui/DeletedFileTracker.java

Index: chrome/android/java/src/org/chromium/chrome/browser/download/ui/DeletedFileTracker.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/download/ui/DeletedFileTracker.java b/chrome/android/java/src/org/chromium/chrome/browser/download/ui/DeletedFileTracker.java
new file mode 100644
index 0000000000000000000000000000000000000000..194c249734d61dd727e82457f946378254dd5495
--- /dev/null
+++ b/chrome/android/java/src/org/chromium/chrome/browser/download/ui/DeletedFileTracker.java
@@ -0,0 +1,47 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.chrome.browser.download.ui;
+
+import java.util.HashSet;
+import java.util.Set;
+import java.util.concurrent.atomic.AtomicInteger;
+
+/**
+ * Tracks items that have been removed from downloads history because they were deleted externally.
+ * For use solely by the {@link DownloadHistoryAdapter}.
+ *
+ * TODO(dfalcantara): Make this class unnecessary.
+ */
+class DeletedFileTracker {
+    private final Set<String> mRegularItems = new HashSet<>();
+    private final Set<String> mIncognitoItems = new HashSet<>();
+    private final AtomicInteger mNumInstances = new AtomicInteger();
+
+    /** Called when a new {@link DownloadHistoryAdapter} is tracking deleted downloads. */
+    void incrementInstanceCount() {
+        mNumInstances.getAndIncrement();
+    }
+
+    /** Called when a {@link DownloadHistoryAdapter} is no longer traking deleted downloads. */
+    void decrementInstanceCount() {
+        if (mNumInstances.decrementAndGet() == 0) {
+            // If there is no interest, clear out the maps so that they stop taking up space.
+            mRegularItems.clear();
+            mIncognitoItems.clear();
+        }
+    }
+
+    /** Add a new item to the tracker. */
+    void add(String id, boolean isOffTheRecord) {
+        Set<String> items = isOffTheRecord ? mIncognitoItems : mRegularItems;
+        items.add(id);
+    }
+
+    /** Checks if an item is in the tracker. */
+    boolean contains(String id, boolean isOffTheRecord) {
+        Set<String> items = isOffTheRecord ? mIncognitoItems : mRegularItems;
+        return items.contains(id);
+    }
+}