Fix chrome_java FindBugs errors found when switching to n sdk.

chrome/android/javatests/src/org/chromium/chrome/browser/crash/CrashTestCase.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.crash;
 
 import android.test.InstrumentationTestCase;
 import android.util.Log;
 
 import java.io.File;
 import java.io.FileWriter;
 import java.io.IOException;
 import java.io.PrintWriter;
-import java.util.Arrays;
-import java.util.List;
 
 /**
  * Base case for Crash upload related tests.
  */
 public class CrashTestCase extends InstrumentationTestCase {
     private static final String TAG = "CrashTestCase";
 
     protected File mCrashDir;
     protected File mCacheDir;
 
     @Override
     protected void setUp() throws Exception {
         super.setUp();
         mCacheDir = getInstrumentation().getTargetContext().getCacheDir();
         mCrashDir = new File(
                 mCacheDir,
                 CrashFileManager.CRASH_DUMP_DIR);
         if (!mCrashDir.isDirectory() && !mCrashDir.mkdir()) {
             throw new Exception("Unable to create directory: " + mCrashDir.getAbsolutePath());
         }
     }
 
     @Override
     protected void tearDown() throws Exception {
         super.tearDown();
-        List<File> crashFiles = Arrays.asList(mCrashDir.listFiles());
+        File[] crashFiles = mCrashDir.listFiles();
+        if (crashFiles == null) {
+            return;

[Ilya Sherman, 2016/10/15 00:02:53]

Please log an error for this case.

+        }
+
         for (File crashFile : crashFiles) {
             if (!crashFile.delete()) {
                 Log.e(TAG, "Unable to delete: " + crashFile.getAbsolutePath());
             }
         }
         if (!mCrashDir.delete()) {
             Log.e(TAG, "Unable to delete: " + mCrashDir.getAbsolutePath());
         }
     }
 
@@ skipping 21 matching lines @@
             }
             minidumpWriter.println(boundary + "--");
             minidumpWriter.flush();
         } finally {
             if (minidumpWriter != null) {
                 minidumpWriter.close();
             }
         }
     }
 }