webapps: Add cleanup task when opening up WebappActivity to clean old web apps

chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappRegistry.java

Index: chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappRegistry.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappRegistry.java b/chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappRegistry.java
index dff54ad1e36ae6b3c2f3b12acefbf6d0b55b8a11..da176539607033caa53dbb8f2edaa27f2892f203 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappRegistry.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappRegistry.java
@@ -28,6 +28,13 @@ public class WebappRegistry {
 
     static final String REGISTRY_FILE_NAME = "webapp_registry";
     static final String KEY_WEBAPP_SET = "webapp_set";
+    static final String KEY_LAST_CLEANUP = "last_cleanup";
+
+    /* Represnts a period of 4 weeks in milliseconds */

[gone, 2015/09/24 10:27:11]

/** Represents a period of 4 weeks in milliseconds. */

[Lalit Maganti, 2015/09/24 12:35:44]

Done.

+    static final long FULL_CLEANUP_DURATION = 4 * 7 * 24 * 60 * 60 * 1000;
+
+    /* Represnts a period of 13 weeks in milliseconds */

[gone, 2015/09/24 10:27:12]

same fix as above.  rename to WEBAPP_UNOPENED_CLEANUP_DURATION?

[Lalit Maganti, 2015/09/24 12:35:44]

Done.

+    static final long WEBAPP_NON_OPEN_CLEANUP_DURATION = 13 * 7 * 24 * 60 * 60 * 1000;
 
     /**
      * Called when a retrieval of the stored web apps occurs.
@@ -81,6 +88,39 @@ public class WebappRegistry {
     }
 
     /**
+     * Deletes the data for all "old" web apps. i.e. webapps which have not been opened by the user

[gone, 2015/09/24 10:27:11]

nit: web apps or webapps.

instead of leaving useful information in just the commit message, put the
information about cleaning up only once a month and deleting apps unused for
three months here.  without any context it's just an opaque blob of heuristics.

[Lalit Maganti, 2015/09/24 12:35:44]

Done.

+     * in a certain period of time.
+     * @param context  Context to open the registry with.
+     */
+    static void unregisterOldWebapps(final Context context) {
+        new AsyncTask<Void, Void, Void>() {
+            @Override
+            protected final Void doInBackground(Void... nothing) {
+                SharedPreferences preferences = openSharedPreferences(context);
+                long currentTime = System.currentTimeMillis();
+                long lastCleanup = preferences.getLong(KEY_LAST_CLEANUP, 0);
+                if (currentTime - lastCleanup < FULL_CLEANUP_DURATION) return null;
+
+                Set<String> currentWebapps = getRegisteredWebappIds(preferences);
+                Set<String> retainedWebapps = new HashSet<String>(currentWebapps);
+                for (String id : currentWebapps) {
+                    long lastUsed = new WebappDataStorage(context, id).getLastUsedTime();
+                    if (currentTime - lastUsed >= WEBAPP_NON_OPEN_CLEANUP_DURATION) {
+                        WebappDataStorage.deleteDataForWebapp(context, id);
+                        retainedWebapps.remove(id);
+                    }
+                }
+
+                preferences.edit()
+                        .putLong(KEY_LAST_CLEANUP, currentTime)
+                        .putStringSet(KEY_WEBAPP_SET, retainedWebapps)
+                        .commit();
+                return null;
+            }
+        }.execute();
+    }
+
+    /**
      * Deletes the data of all web apps, as well as the registry tracking the web apps.
      */
     @VisibleForTesting