[Cleanup] Add an explicit threading assertion.

android_webview/java/src/org/chromium/android_webview/crash/MinidumpUploaderImpl.java

 // Copyright 2016 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.android_webview.crash;
 
 import android.content.Context;
 import android.net.ConnectivityManager;
 import android.net.NetworkInfo;
 import android.webkit.ValueCallback;
@@ skipping 115 matching lines @@
             }
             @Override
             public boolean isUsageAndCrashReportingPermittedByUser() {
                 return mPermittedByUser;
             }
             @Override
             public boolean isUploadEnabledForTests() {
                 // Note that CommandLine/CommandLineUtil are not thread safe. They are initialized
                 // on the main thread, but before the current worker thread started - so this thread
                 // will have seen the initialization of the CommandLine.
+                ThreadUtils.assertOnUiThread();

[Tobias Sargeant, 2017/03/01 08:04:44]

This looks ok, but it's not consistent with the comment (which mentions "this
thread" in a way that says that it might be called on multiple threads). If the
commandline data structure is constant after initialization, do we need restrict
it to a single thread?

                 return CommandLine.getInstance().hasSwitch(
                         CommandLineUtil.CRASH_UPLOADS_ENABLED_FOR_TESTING_SWITCH);
             }
         };
     }
 
     /**
      * Runnable that upload minidumps.
      * This is where the actual uploading happens - an upload job consists of posting this Runnable
      * to the worker thread.
@@ skipping 86 matching lines @@
      * @return whether to reschedule the uploads.
      */
     @Override
     public boolean cancelUploads() {
         setCancelUpload(true);
 
         // Reschedule if there are still minidumps to upload.
         return mFileManager.getAllMinidumpFiles(MAX_UPLOAD_TRIES_ALLOWED).length > 0;
     }
 }