Fix strict mode violation in TabPersistentStore.cleanupPersistentData()

chrome/android/java/src/org/chromium/chrome/browser/compositor/layouts/content/TabContentManager.java

Index: chrome/android/java/src/org/chromium/chrome/browser/compositor/layouts/content/TabContentManager.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/compositor/layouts/content/TabContentManager.java b/chrome/android/java/src/org/chromium/chrome/browser/compositor/layouts/content/TabContentManager.java
index 6b2501ea210c00f73fe6fc7b55f5cb7c85b8fd7b..99401682c7dfd0e6cc88cae9d9b6845cc9b87edf 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/compositor/layouts/content/TabContentManager.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/compositor/layouts/content/TabContentManager.java
@@ -7,6 +7,7 @@ package org.chromium.chrome.browser.compositor.layouts.content;
 import android.content.Context;
 import android.graphics.Bitmap;
 import android.graphics.Canvas;
+import android.os.AsyncTask;
 import android.util.SparseArray;
 import android.view.View;
 
@@ -326,22 +327,31 @@ public class TabContentManager {
      * Remove on-disk thumbnails that are no longer needed.
      * @param modelSelector The selector that answers whether a tab is currently present.
      */
-    public void cleanupPersistentData(TabModelSelector modelSelector) {
+    public void cleanupPersistentData(final TabModelSelector modelSelector) {
         if (mNativeTabContentManager == 0) return;
-        File[] files = PathUtils.getThumbnailCacheDirectory(mContext).listFiles();
-        if (files == null) return;
-
-        for (File file : files) {
-            try {
-                int id = Integer.parseInt(file.getName());
-                if (TabModelUtils.getTabById(modelSelector.getModel(false), id) == null
-                        && TabModelUtils.getTabById(modelSelector.getModel(true), id) == null) {
-                    nativeRemoveTabThumbnail(mNativeTabContentManager, id);
+        new AsyncTask<Void, Void, File[]>() {
+            @Override
+            protected File[] doInBackground(Void... voids) {
+                File thumbnailDirectory = PathUtils.getThumbnailCacheDirectory(mContext);
+                return thumbnailDirectory.listFiles();
+            }
+
+            @Override
+            protected void onPostExecute(File[] files) {
+                for (File file : files) {
+                    try {
+                        int id = Integer.parseInt(file.getName());
+                        if (TabModelUtils.getTabById(modelSelector.getModel(false), id) == null
+                                && TabModelUtils.getTabById(modelSelector.getModel(true), id)
+                                        == null) {
+                            nativeRemoveTabThumbnail(mNativeTabContentManager, id);
+                        }
+                    } catch (NumberFormatException expected) {
+                        // This is an unknown file name, we'll leave it there.
+                    }
                 }
-            } catch (NumberFormatException expected) {
-                // This is an unknown file name, we'll leave it there.
             }
-        }
+        }.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
     }
 
     @CalledByNative