Restore SystemProperties.PROP_NAME_MAX to keep Kindle running.

The limit has been lifted in O, but without this constant, Kindle crashes here:

  Caused by: java.lang.NoSuchFieldException: PROP_NAME_MAX
    at java.lang.Class.getField(Class.java:1607)
    at com.amazon.android.webkit.AmazonWebKitFactories$Implementation.<clinit>(AmazonWebKitFactories.java:59)

The code seems to want to truncate a system property name to avoid the
exception that SystemProperty.get threw if passed a name that was too long.

Bug: http://b/36095274
Test: select a word in Kindle
Change-Id: Id1881a8a7c6386400a1024beb0d1b741bdaefba7