[Suggestions UI] Drop Bitmap references from articles under memory pressure.

base/android/junit/src/org/chromium/base/DiscardableReferencePoolTest.java

+// Copyright 2017 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.base;
+
+import org.junit.Assert;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.robolectric.annotation.Config;
+
+import org.chromium.base.DiscardableReferencePool.DiscardableReference;
+import org.chromium.testing.local.LocalRobolectricTestRunner;
+
+import java.lang.ref.WeakReference;
+
+/**
+ * Tests for {@link DiscardableReferencePool}.
+ */
+@RunWith(LocalRobolectricTestRunner.class)
+@Config(manifest = Config.NONE)
+public class DiscardableReferencePoolTest {
+    /**
+     * Tests that draining the pool clears references and allows objects to be garbage collected.
+     */
+    @Test
+    public void testDrain() {
+        DiscardableReferencePool pool = new DiscardableReferencePool();
+
+        Object object = new Object();
+        WeakReference<Object> weakReference = new WeakReference<>(object);
+
+        DiscardableReference<Object> discardableReference = pool.put(object);
+        Assert.assertEquals(object, discardableReference.get());
+
+        // Drop reference to the object itself, to allow it to be garbage-collected.
+        object = null;
+
+        pool.drain();
+
+        // The discardable reference should be null now.
+        Assert.assertNull(discardableReference.get());
+
+        // The object is not (strongly) reachable anymore, so the weak reference may or may not be
+        // null (it could be if a GC has happened since the pool was drained).
+        // After an explicit GC call it definitely should be null.
+        Runtime.getRuntime().gc();
+
+        Assert.assertNull(weakReference.get());
+    }
+
+    /**
+     * Tests that dropping the (last) discardable reference to an object allows it to be regularly
+     * garbage collected.
+     */
+    @Test
+    public void testReferenceGCd() {
+        DiscardableReferencePool pool = new DiscardableReferencePool();
+
+        Object object = new Object();
+        WeakReference<Object> weakReference = new WeakReference<>(object);
+
+        DiscardableReference<Object> discardableReference = pool.put(object);
+        Assert.assertEquals(object, discardableReference.get());
+
+        // Drop reference to the object itself and to the discardable reference, allowing the object
+        // to be garbage-collected.
+        object = null;
+        discardableReference = null;
+
+        // The object is not (strongly) reachable anymore, so the weak reference may or may not be
+        // null (it could be if a GC has happened since the pool was drained).
+        // After an explicit GC call it definitely should be null.
+        Runtime.getRuntime().gc();
+
+        Assert.assertNull(weakReference.get());
+    }
+}