Downgrade SharedPreferencesManager CheckStyle to warning.

This should be bypassable since any modification in the file triggers
it, not only new usages.

Bug: 1022108
Change-Id: I16fd61b04c9893b7f3b86d8e4e4498894719d523
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1970840Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Henrique Nakashima <hnakashima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#725600}

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

@@ -125,7 +125,7 @@
     </module>
     <module name="RegexpSinglelineJava">
       <property name="id" value="UseSharedPreferencesManagerFromChromeCheck"/>
-      <property name="severity" value="error"/>
+      <property name="severity" value="warning"/>
       <property name="format" value="(getAppSharedPreferences|getDefaultSharedPreferences)"/>
       <property name="ignoreComments" value="true"/>
       <property name="message" value="Use SharedPreferencesManager instead to access app-wide SharedPreferences from //src/chrome."/>