Stop leaking temp directories in SkyShell

At startup, we make a list of all the temp directories that already exist and
then nuke them on a background thread after a five second delay. The five
second delay isn't particularly satisfying, but I think it's wortwhile to get
this work off the critical path of startup.

R=eseidel@chromium.org, eseidel@google.com

Review URL: https://codereview.chromium.org/1228083003 .

engine/src/flutter/shell/BUILD.gn

@@ -100,6 +100,7 @@ if (is_android) {
       "android/org/domokit/sky/shell/GestureProvider.java",
       "android/org/domokit/sky/shell/PlatformServiceProvider.java",
       "android/org/domokit/sky/shell/PlatformViewAndroid.java",
+      "android/org/domokit/sky/shell/ResourceCleaner.java",
       "android/org/domokit/sky/shell/ResourceExtractor.java",
       "android/org/domokit/sky/shell/ServiceFactory.java",
       "android/org/domokit/sky/shell/ServiceRegistry.java",

engine/src/flutter/shell/android/org/domokit/sky/shell/ResourceCleaner.java

@@ -0,0 +1,86 @@
+// 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.domokit.sky.shell;
+
+import android.content.Context;
+import android.os.AsyncTask;
+import android.os.Handler;
+import android.util.Log;
+
+import java.io.File;
+import java.io.FilenameFilter;
+
+/**
+ * A class to clean up orphaned resource directories after unclean shutdowns.
+ **/
+public class ResourceCleaner {
+    private static final String TAG = "ResourceCleaner";
+    private static final String TEMPORARY_RESOURCE_PREFIX = ".org.chromium.Chromium.";
+    private static final long DELAY_MS = 5000;
+
+    private class CleanTask extends AsyncTask<Void, Void, Void> {
+        private final File[] mFilesToDelete;
+
+        public CleanTask(File[] filesToDelete) {
+            mFilesToDelete = filesToDelete;
+        }
+
+        public boolean hasFilesToDelete() {
+            return mFilesToDelete.length > 0;
+        }
+
+        @Override
+        protected Void doInBackground(Void... unused) {
+            Log.i(TAG, "Cleaning " + mFilesToDelete.length + " resources.");
+            for (File file : mFilesToDelete) {
+                if (file.exists()) {
+                    deleteRecursively(file);
+                }
+            }
+            return null;
+        }
+
+        private void deleteRecursively(File parent) {
+            if (parent.isDirectory()) {
+                for (File child : parent.listFiles()) {
+                    deleteRecursively(child);
+                }
+            }
+            parent.delete();
+        }
+    }
+
+    private final Context mContext;
+
+    public ResourceCleaner(Context context) {
+        mContext = context;
+    }
+
+    public void start() {
+        File cacheDir = mContext.getCacheDir();
+        if (cacheDir == null) {
+            return;
+        }
+
+        final CleanTask task = new CleanTask(cacheDir.listFiles(new FilenameFilter() {
+            @Override
+            public boolean accept(File dir, String name) {
+                boolean result = name.startsWith(TEMPORARY_RESOURCE_PREFIX);
+                return result;
+            }
+        }));
+
+        if (!task.hasFilesToDelete()) {
+            return;
+        }
+
+        new Handler().postDelayed(new Runnable() {
+            @Override
+            public void run() {
+                task.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
+            }
+        }, DELAY_MS);
+    }
+}

engine/src/flutter/shell/android/org/domokit/sky/shell/SkyApplication.java

@@ -68,7 +68,9 @@ public class SkyApplication extends BaseChromiumApplication {
     }
 
     private void initResources() {
-        mResourceExtractor = new ResourceExtractor(getApplicationContext());
+        Context context = getApplicationContext();
+        new ResourceCleaner(context).start();
+        mResourceExtractor = new ResourceExtractor(context);
         onBeforeResourceExtraction(mResourceExtractor);
         mResourceExtractor.start();
     }