Upstream oodles of Chrome for Android code into Chromium.

chrome/android/java_staging/src/org/chromium/chrome/browser/webapps/WebappManagedActivity.java

+// Copyright 2015 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.webapps;
+
+import java.io.File;
+
+/**
+ * Type of WebappActivity that has the ability to swap out the webapp it is currently showing for a
+ * new one. This is necessary on Android versions older than L because the framework had no way of
+ * allowing multiple instances of an Activity to be launched and show up as different tasks.
+ * Anything extending this class must be named WebappActivity0, WebappActivity1, etc.
+ */
+public abstract class WebappManagedActivity extends WebappActivity {
+    private final int mActivityIndex;
+
+    public WebappManagedActivity() {
+        mActivityIndex = getActivityIndex();
+    }
+
+    @Override
+    public void onStartWithNative() {
+        super.onStartWithNative();
+
+        if (!isFinishing()) {
+            markActivityUsed();
+        }
+    }
+
+    @Override
+    protected File getActivityDirectory() {
+        return WebappDirectoryManager.getWebappDirectory(String.valueOf(mActivityIndex));
+    }
+
+    /**
+     * Marks that this WebappActivity is recently used to prevent other webapps from using it.
+     */
+    private void markActivityUsed() {
+        ActivityAssigner.instance(this).markActivityUsed(mActivityIndex, getWebappInfo().id());
+    }
+
+    /**
+     * Pulls out the index of the WebappActivity subclass that is being used.
+     * e.g. WebappActivity0.getActivityIndex() will return 0.
+     * @return The index corresponding to this WebappActivity.
+     */
+    private int getActivityIndex() {
+        // Cull out the activity index from the class name.
+        String baseClassName = WebappActivity.class.getSimpleName();
+        String className = this.getClass().getSimpleName();
+        assert className.matches("^" + baseClassName + "[0-9]+$");
+        String indexString = className.substring(baseClassName.length());
+        return Integer.parseInt(indexString);
+    }
+}