⛲ Add presubmit to prevent SharedPreferences misuse.

tools/android/checkstyle/chromium-style-5.0.xml

 <?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE module PUBLIC "-//Puppy Crawl//DTD Check Configuration 1.3//EN" "http://www.puppycrawl.com/dtds/configuration_1_3.dtd">
 
 <!--
   See installation instructions: https://sites.google.com/a/chromium.org/dev/checkstyle
 -->
 <module name="Checker">
   <property name="severity" value="warning"/>
   <property name="charset" value="UTF-8"/>
+  <module name="SuppressionFilter">
+    <property name="file" value="tools/android/checkstyle/suppressions.xml"/>
+  </module>
   <module name="TreeWalker">
     <module name="AvoidStarImport">
       <property name="severity" value="error"/>
     </module>
     <module name="IllegalCatch">
       <property name="severity" value="info"/>
     </module>
     <module name="RedundantImport">
       <message key="import.redundant" value="Redundant import: {0}. Use :JavaImportOrganize (ECLIM) or Ctrl+Shift+O (Eclipse) to sort imports"/>
       <property name="severity" value="error"/>
@@ skipping 181 matching lines @@
       <property name="format" value="StringBuffer"/>
       <property name="ignoreComments" value="true"/>
       <property name="message" value="Avoid StringBuffer; use StringBuilder instead, which is faster (it's not thread-safe, but this is almost never needed)"/>
     </module>
     <module name="RegexpSinglelineJava">
       <property name="severity" value="warning"/>
       <property name="format" value="android\.app\.AlertDialog"/>
       <property name="ignoreComments" value="true"/>
       <property name="message" value="Avoid android.app.AlertDialog; if possible, use android.support.v7.app.AlertDialog instead, which has a Material look on all devices. (Some parts of the codebase can’t depend on the support library, in which case android.app.AlertDialog is the only option)"/>
     </module>
+    <module name="RegexpSinglelineJava">
+      <property name="id" value="SharedPreferencesCheck"/>
+      <property name="severity" value="error"/>
+      <property name="format" value="getDefaultSharedPreferences"/>
+      <property name="ignoreComments" value="true"/>
+      <property name="message" value="Use ContextUtils.getAppSharedPreferences() instead to access app-wide SharedPreferences."/>
+    </module>
   </module>
 
   <!-- Non-TreeWalker modules -->
   <module name="FileTabCharacter">
     <property name="severity" value="error"/>
   </module>
   <module name="RegexpSingleline">
     <property name="severity" value="error"/>
     <property name="format" value="[ \t]+$"/>
     <property name="message" value="Trailing whitespace"/>
   </module>
   <module name="RegexpHeader">
     <property name="severity" value="error"/>
     <property name="header" value="^// Copyright 20\d\d The Chromium Authors. All rights reserved.$\n^// Use of this source code is governed by a BSD-style license that can be$\n^// found in the LICENSE file.$"/>
   </module>
 </module>